cp's OEIS Frontend

A221583 A sum over partitions (q=18), see first comment.

%I A221583 #17 Feb 24 2022 08:45:12
%S A221583 1,17,323,5814,104958,1889227,34011900,612213877,11019954438,
%T A221583 198359179578,3570467115834,64268408079198,1156831379431973,
%U A221583 20822964829665048,374813367546080412,6746640615829343087,121439531095946141922,2185911559727028566514
%N A221583 A sum over partitions (q=18), see first comment.
%C A221583 Set q=18 and f(m)=q^(m-1)*(q-1), then a(n) is the sum over all partitions P of n over all products Product_{k=1..L} f(m_k) where L is the number of different parts in the partition P=[p_1^m_1, p_2^m_2, ..., p_L^m_L].
%C A221583 Setting q to a prime power gives the sequence "Number of conjugacy classes in GL(n,q)":
%C A221583   q=3: A006952, q=4: A049314, q=5: A049315, q=7: A049316, q=8: A182603,
%C A221583   q=9: A182604, q=11: A182605, q=13: A182606, q=16: A182607, q=17: A182608,
%C A221583   q=19: A182609, q=23: A182610, q=25: A182611, q=27: A182612.
%C A221583 Sequences where q is not a prime power:
%C A221583   q=6: A221578, q=10: A221579, q=12: A221580,
%C A221583   q=14: A221581, q=15: A221582, q=18: A221583, q=20: A221584.
%H A221583 Alois P. Heinz, <a href="/A221583/b221583.txt">Table of n, a(n) for n = 0..300</a>
%p A221583 with(numtheory):
%p A221583 b:= proc(n) b(n):= add(phi(d)*18^(n/d), d=divisors(n))/n-1 end:
%p A221583 a:= proc(n) a(n):= `if`(n=0, 1,
%p A221583        add(add(d*b(d), d=divisors(j)) *a(n-j), j=1..n)/n)
%p A221583     end:
%p A221583 seq(a(n), n=0..30);  # _Alois P. Heinz_, Feb 03 2013
%t A221583 b[n_] := Sum[EulerPhi[d]*18^(n/d), {d, Divisors[n]}]/n-1; a[n_] := a[n] = If[n == 0, 1, Sum[Sum[d*b[d], {d, Divisors[j]}]*a[n-j], {j, 1, n}]/n]; Table[a[n], {n, 0, 30}] (* _Jean-François Alcover_, Feb 17 2014, after _Alois P. Heinz_ *)
%o A221583 (PARI)
%o A221583 N=66; x='x+O('x^N);
%o A221583 gf=prod(n=1,N, (1-x^n)/(1-18*x^n)  );
%o A221583 v=Vec(gf)
%K A221583 nonn
%O A221583 0,2
%A A221583 _Joerg Arndt_, Jan 20 2013