A178607 Largest prime < n!! (double factorial of n).

2, 7, 13, 47, 103, 383, 941, 3833, 10391, 46073, 135131, 645097, 2027023, 10321919, 34459423, 185794463, 654729073, 3715891181, 13749310511, 81749606383, 316234143163, 1961990553581, 7905853580621, 51011754393599

Offset: 3

Author

Vladimir Joseph Stephan Orlovsky, May 30 2010

Keywords

• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 3..200

Crossrefs

Cf. A006882, A006990, A037151, A178606.

Programs

Mathematica

PrimePrev[n_]:=Module[{k},k=n-1;While[ !PrimeQ[k],k-- ];k]; Table[PrimePrev[n!! ],{n,3,40}]
NextPrime[#,-1]&/@(Range[3,30]!!) (* Harvey P. Dale, Jul 13 2015 *)

PARI

a(n)=if(n<2, 1, n*a(n-2)); for(n=3,26,print1(precprime(a(n)-1)", ")); \\ Graziano Aglietti (mg5055(AT)mclink.it), Aug 23 2010

Formula

a(n) = A151799(A006882(n)). - R. J. Mathar, Jun 23 2010

Extensions

Offset corrected by R. J. Mathar, Jun 23 2010