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

3,1

Links

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

Formula

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

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 *)

Prog

(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

Crossrefs

Cf. A006882, A006990, A037151, A178606.

Sequence in context: A262727 A129592 A153136 * A321407 A127487 A226140

Adjacent sequences: A178604 A178605 A178606 * A178608 A178609 A178610

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, May 30 2010

Extensions

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

Status

approved