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

4 votes

On Pell's equation

Partial answer to (2). The smallest solution in some cases might be prohibitively large. Check this paper pp 3,4. It uses negative Pell, but its solution is smaller that the wanted. The paper show …
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-1 votes

A quadrant of residues

Partial answer giving probabilistic algorithm under assumptions which can be greatly relaxed. wlog assume $AB$ is the smallest product. Write $$ r_1= xz \mod A \qquad (1)$$ $$ r_2= xy \mod B \qquad …
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2 votes

On the mixed sum of three k-th powers

EDIT This answers previous revision, quite different question. Let $k = 5$. I think a single representation outside your forbidden congruences would violate "Vojta's more general abc conjecture". …
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7 votes
Accepted

Calculating (n ^ fibonacci(k)) MOD m for a large value of k

Assuming $n$ and $m$ are coprime and $m$ is factored, first compute $a=\text{fibonacci}(k) \mod \varphi(m)$. Computing linear recurrence efficiently modulo $n$ is possible, e.g. via matrix exponentiat …
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11 votes

Efficient computation of integer representation as a sum of three squares

A modification of Dror's comment. This probabilistic algorithm worked for me. The main idea is to pick some $z$, compute $m=n - z^2$, factor $m$ with trial division and express it as a sum of two sq …
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17 votes

Can four integer numbers $x$, $y$, $x-y$, $x+y$ be powerful numbers where $\gcd(x,y)=1$?

Using the infinitely many rational points on the curve $x^4-y^4=(2^4-1) y^2 z^2$, the smallest solution we found is with $x$ having 146 decimal digits (smaller solutions may exist). Using the same cur …
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0 votes

Transformation of a bivariate polynomial into a homogeneous one

Edit corrected major mistake One approach is to work symbolically and solve a system over the rationals. Choose bounds for the degrees of $S,T,H$ and write them as $\sum a_m x^i y^j$ where each $a_m …
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4 votes

What are the solutions in numbers of $xyz \mid x^n + y^n + z^n$, $x,y,z$ globally coprime

Some solutions for $n=7$: n=7;y=2;z=3;x_i=[1, 463, -5, -2315] n=7;y=2;z=5;x_i=[78253, -7, -1597] n=7;y=2;z=7;x_i=[-9, -639, -11601, -823671] n=7;y=2;z=9;x_i=[-11, -4783097] n=7;y=2;z=11;x_i=[559, 1499 …
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2 votes

Equivalence between Diffie Hellman and Discrete Log

If the Discrete Log is easy, so is computationally DH. According to: Difiie-Hellman is as Strong as Discrete Log for Certain Primes they [DH] conjectured that breaking their scheme would be as ha …
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0 votes
Accepted

Explicit bivariate quadratic polynomials where Coppersmith is better than standard solver?

Partial answer about "regular diophantine solver". Finding points on conics in general require integer factorization. Several papers deal with points on $a x^2+b y^2=c z^2$ and they require factoriz …
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0 votes

Computing (on a computer) the first few (non-trivial) zeros of the zeta function of a number...

First we observed that $\zeta_K$ numerically has double zero at $1/2$ and asked question about it. In comment, David E Speyer suggested $L(s,\chi)^2$ should divide $\zeta_K$. We believe that all zeros …
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