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a(n) = Sum_{d|n} d^(n^2/d).
2

%I #19 Jun 10 2019 08:34:04

%S 1,5,28,513,3126,840242,823544,8606711809,7625984905477,

%T 1221277338483250,285311670612,89215914432866222355906,

%U 302875106592254,316913110043605007120962336162,608295209422788113565012727970423808,680564733921105089459460296530789924865

%N a(n) = Sum_{d|n} d^(n^2/d).

%H Seiichi Manyama, <a href="/A308593/b308593.txt">Table of n, a(n) for n = 1..80</a>

%t Table[Sum[d^(n^2/d), {d, Divisors[n]}], {n,1,20}] (* _Vaclav Kotesovec_, Jun 09 2019 *)

%o (PARI) {a(n) = sumdiv(n, d, d^(n^2/d))}

%Y Diagonal of A308509.

%Y Cf. A023887, A055225, A308571.

%K nonn

%O 1,2

%A _Seiichi Manyama_, Jun 09 2019