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a(n) = ((n+1)^(n^2) - 1)/n^3.
2

%I #6 Jun 06 2021 19:24:21

%S 1,10,9709,2384185791,227442304239437611,

%T 12276531693794691998976960100,

%U 520133998799548061610162525309582775649689,23027704253395670256876704807446325518902757016163752166205

%N a(n) = ((n+1)^(n^2) - 1)/n^3.

%F a(n) = ((n+1)^(n^2) - 1)/n^3.

%t Table[ ((n + 1)^(n^2) - 1)/n^3, {n, 1, 10} ]

%Y Cf. A137642 (((p+1)^(p^2) - 1)/p^3 for p = prime(n)).

%Y Cf. A133591 (((p-1)^(p^2) + 1)/p^3 for p = prime(n)).

%K nonn

%O 1,2

%A _Alexander Adamchuk_, Jan 31 2008