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URL: https://oeis.org/A374979

⇱ A374979 - OEIS

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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).
2
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
1,7
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
LINKS
FORMULA
Sum_{k=1..n} a(k) ~ Pi^12 * n^12 / 22348298649600. - Vaclav Kotesovec, Sep 20 2024
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
MATHEMATICA
b[n_, k_] := b[n, k] = If[k == 0, If[n == 0, 1, 0], If[k == 1, If[n == 0, 0, DivisorSigma[1, n]], Function[q, Sum[b[j, q]*b[n-j, k-q], {j, 0, n}]][Quotient[k, 2]]]];
a[n_] := b[n, 6];
Table[a[n], {n, 1, 35}] (* Jean-François Alcover, Sep 13 2025 after Alois P. Heinz *)
PROG
(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))
CROSSREFS
KEYWORD
nonn
AUTHOR
Chai Wah Wu, Jul 26 2024
STATUS
approved