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Primes of the form A004154(n) - 1.
4

%I #13 Aug 07 2015 02:40:21

%S 5,23,11,71,503,62270207,871782911,121645100408831,243290200817663,

%T 304888344611713860501503,137637530912263450463159795815809023

%N Primes of the form A004154(n) - 1.

%C More precisely, scan A004154, subtract 1 and record the answer if it is a prime. The sequence is not monotonic.

%H Charles R Greathouse IV, <a href="/A078190/b078190.txt">Table of n, a(n) for n = 1..17</a>

%p A004154 := proc(n) option remember ; local m ; if n <= 1 then RETURN(1) ; else m := A004154(n-1)*n ; while m mod 10 = 0 do m := m /10 ; end ; RETURN(m) ; fi ; end: n := 1 ; while true do f := A004154(n) : if isprime(f-1) then printf("%d, ",f-1) ; fi ; n := n+1 : od : # _R. J. Mathar_, Feb 27 2007

%o (PARI) v=[];for(n=1,500,if(ispseudoprime(t=n!/10^valuation(n!,5)-1),v=concat(v,t))); v \\ _Charles R Greathouse IV_, Feb 14 2011

%Y Cf. A004154, A078154, A078203, A078305.

%K nonn

%O 1,1

%A _Cino Hilliard_, Dec 23 2002

%E More terms from _R. J. Mathar_, Feb 27 2007