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Computational Number Theory is for explicit calculations or algorithms involving anything of interest to number theorists.

-1 votes
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Analog of ceil and floor of $\sqrt{a(a+1)}$ in modular arithmetic

If we take ceil and floor of $\sqrt{x(x+1)}$ (when it exists) we get $x$ and $x+1$ respectively. Is there an analog of this assuming roots exist in modular arithmetic (at least modulo primes)? Assumin …
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0 votes
0 answers
58 views

Factoring totient of a prime

Is it any easy to factor $p-1$ when $p$ is a prime compared to general factorization problem? What about when $2p+1$ is also a prime?
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1 vote
0 answers
104 views

Simultaneous elimination of variables in multiple polynomials

I have a system of $n=O(1)$ non-homogeneous polynomials of total degree $d=O(1)$ $p_1,\dots,p_r\in \mathbb Z[x_1,\dots,x_n]$. I would like to eliminate $n-1$ variables simultaneously from the $n$ poly …
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2 votes
1 answer
103 views

On square root modulo $2^t-1$

Is there a way to compute an $x$ satisfying $$x^2\equiv a\bmod(2^t-1)$$ where $a,t$ are integers given to us and factorization of $2^t-1$ is not given to us?
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1 vote
0 answers
34 views

Does $2$ variable linear Diophantine equation in $NC$ imply $2$ dimensional shortest vector ...

Consider the Linear Diophantine in known $a,b,c\in\mathbb Z$ $$ax+by=c.$$ Above can be solve by Extended Euclidean which is not in $NC$ as far as we know. It is clear if Extended Euclidean is in $NC$ …
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1 vote
0 answers
133 views

Quadratic equations over Gaussian integers

Given an equation $x^2\equiv(a+ib)\bmod(c+id)$ where $a,b,c,d\in\mathbb Z$ holds, how to test if the equation has solutions and how to find the solutions in polynomial in $\log(|abcd|)$ time if $c+id$ …
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0 votes
0 answers
73 views

Using coppersmith for bounded solution of a short linear Diophantine problem

I have a $3$-variable linear Diophantine equation $$ax+by+cz=r$$ where $a,b,c,r\in\mathbb Z$ are known and can be as large in magnitude as needed and I know the equation has a solution $x,y,z\in\mathb …
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2 votes
0 answers
214 views

Modular inverse computation - avoiding Euclidean algorithm

Modular inverse is known to be computable by Extended Euclidean algorithm which is the reaping the rewards of computing the GCD of two numbers or proving two numbers are coprime. If we already know t …
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5 votes
1 answer
309 views

Parity of number of solutions to Diophantine equations

By $MRDP$ resolution of Hilbert's tenth, we infer, counting number of solutions to Diophantine equations is undecidable. Is parity of number of solutions to Diophantine equations undecidable?
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Will an integer program to deterministically factor integers help derandomize $\mathbb F_q[x...

There are many analogies between the objects $\mathbb F_q[x]$ and $\mathbb Z$. Supposing there is a fixed (say $10^9$) dimension linear integer program (describable without any objective function) in …
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2 votes
1 answer
476 views

Modular square roots problem which is $NP$ hard

It is well known extracting modular square roots modulo a composite number factors the modulus. On other hand given $u,v>0$ and an integer $n$, deciding if there is a factor of $n$ in $[u,v]$ is $NP$ …
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1 vote
0 answers
69 views

Is this factorization problem in EXP?

Factorization is not known to have a polynomial time algorithm. Traditionally the input length is number of bits in representation of the integer to be factored. However now consider integers of form …
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2 votes
0 answers
197 views

On GCD and lattice reduction

$LLL$ algorithm is vectorized version of Euclidean algorithm for $GCD$. Even the $m=2$ case known to Lagrange and Gauss does not have an $NC$ algorithm for shortest vector. If $GCD$ is in $NC$ and in …
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4 votes
0 answers
104 views

Questions in number theory related to $NC$ and $P$-completeness

Given $a,b\in\mathbb N$ find $\operatorname{GCD}(a,b)$. Given $a,b,c\in\mathbb N$ find $x,y\in\mathbb Z$ such that $ax+by=c$. Euclidean algorithm solves both. My question is if either 1 or 2 is i …
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1 vote
1 answer
225 views

Software tools to find square root modulo $2^t$

Are there any software tools to find modular square roots of $y$ in $$x^2\equiv y\bmod p^t$$ where $p$ is a prime $\geq2$? Are there any special techniques which can speed up at $p=2$?
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