Original entry on oeis.org
2, 3, 7, 13, 73, 871782913, 1307674369, 62044840173323943937, 33078854415193864122595302822125378214568325182093497117061192683541123570097156545925087233
Offset: 1
Original entry on oeis.org
5, 23, 11, 71, 503, 62270207, 871782911, 121645100408831, 243290200817663, 304888344611713860501503, 137637530912263450463159795815809023
Offset: 1
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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
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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
A078203
Numbers k such that A004154(k) + 1 is prime.
Original entry on oeis.org
1, 2, 3, 5, 6, 14, 15, 24, 74, 191, 222, 276, 2200, 3041, 3701, 4324, 6201
Offset: 1
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f[n_] := n!/10^Sum[ Floor[n/5^k], {k, 1, Log[10, n] + 1}]; Do[ If[ PrimeQ[ f[n] + 1], Print[n]], {n, 1, 850}]
A079154
Numbers k such that reverse(A004154(k)) - 1 is prime.
Original entry on oeis.org
3, 4, 12, 30, 33, 1406
Offset: 1
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f[n_] := n!/10^Sum[Floor[n/5^k], {k, 1, Log[10, n] + 1}]; Do[ If[ PrimeQ[ FromDigits[ Reverse[ IntegerDigits[ f[n]]]] - 1], Print[n]], {n, 1, 800}]
Showing 1-4 of 4 results.
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