editing

approved

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

approved

editing

_Cino Hilliard (hillcino368(AT)gmail.com), _, Dec 23 2002

_Charles R Greathouse IV_, , <a href="/A078190/b078190.txt">Table of n, a(n) for n = 1..17</a>

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

(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

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 (mathar(AT)strw.leidenuniv.nl), _, Feb 27 2007

More terms from _R. J. Mathar (mathar(AT)strw.leidenuniv.nl), _, Feb 27 2007

proposed

approved

5, 23, 11, 71, 503, 62270207, 871782911, 121645100408831, 243290200817663, 304888344611713860501503, 137637530912263450463159795815809023, 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916863

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

(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

easy,nonn

nonn

approved

proposed

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

easy,nonn,new

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 : - Richard R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Feb 27 2007

easy,nonn,new

More terms from Richard R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Feb 27 2007