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  • Let $a(n)$ be A266328 i.e. an integer sequence with exponential generating function $$ A(x)=\exp\int B(x) \,dx $$ such that $$ B(x)=\exp(-x)\exp\int A(x) \,dx $$ where the constant of integration is zero.
  • Let $$ R(n,q,m)=R(n-1,q+1,m)+\sum\limits_{j=0}^{q-m} \binom{q+1}{j}R(n-1,j,m), \\ R(0,q,m)=1. $$

I conjecture that $$ R(n,0,0)=(n+1)!, \\ R(n,0,1)=a(n+1). $$

Here is the PARI/GP prog to check it numerically:

a(n) = my(A=1+x, B=1+x); for(i=0, n, A = exp( intformal( B + x*O(x^n) ) ); B = exp( intformal( A - 1 ) ) ); n!*polcoeff(A, n)
R_upto(n,m)=my(v1, v2, v3, v4); v1=vector(n+1, i, 1); v2=v1; v3=vector(n+1, i, 0); v3[1]=1; v4=vector(n, i, vector(i+1, j, binomial(i, j-1))); for(i=1, n, for(q=0, (n-i), v2[q+1]=v1[q+2]+sum(j=0, q-m, v4[q+1][j+1]*v1[j+1])); v1=v2; v3[i+1]=v1[1]); v3
test1(n)=vector(n+1, i, i!)==R_upto(n, 0)
test2(n)=vector(n+1, i, a(i))==R_upto(n, 1)

Is there a way to prove it? Is there a way to find exponential generating functions for $b(n,m)=R(n-1,0,m)$ with $b(0,m)=1$ and where $m\in\mathbb N$? Of course, here you may answer only the first question (and I am ready to choose such an answer as the correct one).

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    $\begingroup$ What does "the constant of integration is $0$" mean? It seems to rely on a distinguished choice of 'best' anti-derivative. \\ I assumed "you can only answer the first question" (whose common reading is "you are not capable of answering the second question") should be "you may answer only the first question" (one common reading of which is "it is OK to answer only the first question"), and edited accordingly. $\endgroup$
    – LSpice
    Commented Jul 13, 2023 at 20:51
  • $\begingroup$ @LSpice, thank you for comment and for editing too! I don't know much about integrals, so I took the definition of $A(x)$ from A266328. $\endgroup$ Commented Jul 14, 2023 at 7:37
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    $\begingroup$ Re, the descriptive text in A266328 seems to say that both $A$ and $B$ are expandable in Taylor series about $0$ with $A(0) = 1$ and $B(0) = 1$. Since $\log(A(x))$ is Integral B(x), it seems to me that this must mean $\log(A(x)) = \int_0^x B(x)\mathrm dx$. $\endgroup$
    – LSpice
    Commented Jul 14, 2023 at 13:15

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