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%I #18 Jul 20 2021 07:00:40
%S 1,2,4,2428957
%N Index of factorial primes of the form k! + 1.
%F a(n) = PrimePi(A002981(n)!+1).
%e The exact subscript of the 5th prime [1 + 27! = 10888869450418352160768000001] is not yet available.
%Y Cf. A000720, A002981, A002982, A055490, A088332.
%K hard,nonn,more
%O 1,2
%A _Labos Elemer_, Jul 11 2001
%E Offset 1 from _Michel Marcus_, Aug 29 2019
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