OFFSET
1,2
LINKS
James Mitchell, Table of n, a(n) for n = 1..100
P. J. Cameron, M. Gadouleau, J. D. Mitchell, Y. Peresse, Chains of subsemigroups, arXiv preprint arXiv:1501.06394 [math.GR], 2015.
MATHEMATICA
b[n_] := If[n < 1, 0, PrimeOmega[n]];
a[n_] := -2 - n + Sum[Binomial[n, i]*(b[i] + (Binomial[n, i] - 1)*i/2 + 2), {i, 0, n}];
Array[a, 28] (* Jean-François Alcover, Feb 19 2019, from PARI *)
PROG
(PARI) b(n)=if(n<1, 0, bigomega(n)) /* A001222 */
a(n)=-2-n+sum(i=0, n, binomial(n, i)*(b(i)+(binomial(n, i)-1)*i/2+2))
CROSSREFS
KEYWORD
nonn
AUTHOR
James Mitchell, May 14 2014
STATUS
approved