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%I #7 Aug 07 2025 12:29:37
%S 1,3,39,12207,2384185791,181898940354585647583,
%T 2117582368135750847670806251699104905128479,
%U 573971850987445072250359637315549647372395291392620860111695169081258427468128502368927
%N a(n) = (5^(2^n) - 1)/2^(n+2).
%t Table[(5^(2^n)-1)/2^(n+2),{n,0,10}] (* _Harvey P. Dale_, Aug 07 2025 *)
%Y Cf. A070632.
%K nonn
%O 0,2
%A _Lekraj Beedassy_, Aug 21 2004