OFFSET
1,4
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..4240
N. J. A. Sloane, Transforms
MATHEMATICA
a[1] = a[2] = 1; a[n_] := a[n] = Sum[DivisorSigma[0, (n - 2)/d] a[d], {d, Divisors[n - 2]}]; Table[a[n], {n, 65}]
PROG
(PARI) A319133(n) = if(n<=2, 1, sumdiv(n-2, d, numdiv((n-2)/d)*A319133(d))); \\ (non-memoized implementation) - Antti Karttunen, Sep 11 2018
(PARI)
\\ Faster implementation:
up_to = 4240;
A319133list(up_to) = { my(u=vector(up_to)); u[1] = u[2] = 1; for(n=3, up_to, u[n] = sumdiv(n-2, d, numdiv((n-2)/d)*u[d])); (u); };
v319133 = A319133list(up_to);
A319133(n) = v319133[n]; \\ Antti Karttunen, Sep 11 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Sep 11 2018
STATUS
approved