This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
[a: n in [1..100] | IsPrime(a) where a is Factorial(n) div 10^Valuation(Factorial(n), 5)+1]; // Vincenzo Librandi, Jun 03 2016
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
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
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, 750}]
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, 0, 800}]
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