cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A374979 a(n) = Sum_{i+j+k+l+m+r=n, i,j,k,l,m,r >= 1} sigma(i)*sigma(j)*sigma(k)*sigma(l)*sigma(m)*sigma(r).

Original entry on oeis.org

0, 0, 0, 0, 0, 1, 18, 159, 942, 4281, 16050, 51932, 149532, 391524, 947246, 2143677, 4581204, 9316195, 18138636, 33984912, 61534652, 108055425, 184582014, 307515038, 500798058, 798762453, 1249917936, 1921788036, 2907159804, 4332046200, 6365441400, 9232216725
Offset: 1

Views

Author

Chai Wah Wu, Jul 26 2024

Keywords

Comments

6-fold convolution of A000203.
Convolution of A000203 and A374978.
a(n) = Sum_{i=1..n-1} A000203(i)*A374978(n-i).
a(n) = Sum_{i=1..n-2} A000385(i)*A374977(n-i-1).
a(n) = Sum_{i=1..n-1} A374951(i)*A374951(n-i).
a(n) = Sum_{i+j+k=n-3, i,j,k>=1} A000385(i)*A000385(j)*A000385(k).
Column k=6 of A319083.
In general, if the sequence "a" is a k-fold convolution of A000203, then Sum_{k=1..n} a(k) ~ Pi^(2*k) * n^(2*k) / (6^k * (2*k)!). - Vaclav Kotesovec, Sep 20 2024

Crossrefs

Programs

  • Maple
    b:= proc(n, k) option remember; `if`(k=0, `if`(n=0, 1, 0),
          `if`(k=1, `if`(n=0, 0, numtheory[sigma](n)), (q->
           add(b(j, q)*b(n-j, k-q), j=0..n))(iquo(k, 2))))
        end:
    a:= n-> b(n, 6):
    seq(a(n), n=1..55);  # Alois P. Heinz, Jul 26 2024
  • Python
    from functools import lru_cache
    from sympy import divisor_sigma
    def A374979(n):
        @lru_cache(maxsize=None)
        def g(x):
            f = factorint(x+1).items()
            return(5*prod((p**(3*(e+1))-1)//(p**3-1) for p,e in f)-(5+6*x)*prod((p**(e+1)-1)//(p-1) for p, e in f))//12
        return sum(g(i)*g(j)*g(n-3-i-j) for i in range(1,n-4) for j in range(1,n-i-3))

Formula

Sum_{k=1..n} a(k) ~ Pi^12 * n^12 / 22348298649600. - Vaclav Kotesovec, Sep 20 2024