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%I #7 Jun 08 2021 02:29:20
%S 19,9007199254741,392750863685502459010271914701912679
%N a(n) = ((p-1)^(p^2) + 1)/p^3 where p = prime(n).
%t Table[ ((Prime[n] - 1)^(Prime[n]^2) + 1)/Prime[n]^3, {n,2,10} ]
%Y Subset of A137643.
%K nonn,bref
%O 2,1
%A _Alexander Adamchuk_, Dec 27 2007