A139421 a(1)=1; for n>1, a(n) = largest prime divisor of n!!.

1, 2, 3, 2, 5, 3, 7, 3, 7, 5, 11, 5, 13, 7, 13, 7, 17, 7, 19, 7, 19, 11, 23, 11, 23, 13, 23, 13, 29, 13, 31, 13, 31, 17, 31, 17, 37, 19, 37, 19, 41, 19, 43, 19, 43, 23, 47, 23, 47, 23, 47, 23, 53, 23, 53, 23, 53, 29, 59, 29, 61, 31, 61, 31, 61, 31, 67, 31, 67, 31, 71, 31, 73, 37

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Formula

a(n) = A006530(A006882(n)). - Michel Marcus, Nov 08 2013

Mathematica

a = {}; Do[b = First[Last[FactorInteger[n!! ]]]; AppendTo[a, b], {n, 2, 100}]; a
FactorInteger[#][[-1, 1]]&/@(Range[80]!!) (* Harvey P. Dale, Feb 15 2014 *)

Crossrefs

Cf. A010693.

Sequence in context: A331634 A370833 A341676 * A219964 A165500 A341679

Adjacent sequences: A139418 A139419 A139420 * A139422 A139423 A139424

Keyword

nonn

Author

Artur Jasinski, Apr 21 2008

Status

approved