A133992 a(n) = tau( prime(n)*prime(prime(n)) - 1 ).

2, 4, 8, 4, 12, 12, 8, 16, 18, 16, 24, 30, 8, 6, 12, 12, 4, 24, 72, 8, 32, 8, 24, 24, 6, 8, 24, 16, 8, 64, 16, 8, 36, 16, 8, 24, 16, 48, 16, 24, 6, 24, 8, 16, 6, 12, 16, 4, 32, 24, 8, 48, 16, 16, 6, 16, 8, 16, 12, 24, 18, 24, 40, 96, 16, 16, 72, 24, 8, 16, 36, 16, 8, 16, 16, 48, 16, 48, 48, 8

Offset

1,1

Links

Table of n, a(n) for n=1..80.

Formula

a(n) = A000005(A073065(n)-1).

Maple

A133992 := proc(n) p := ithprime(n) ; p*ithprime(p)-1 ; numtheory[tau](%) ; end proc: seq(A133992(n), n=1..80) ; # R. J. Mathar, Jun 28 2010

Mathematica

Table[DivisorSigma[0, Prime[n]*Prime[Prime[n]] - 1], {n, 100}] (* Wesley Ivan Hurt, Feb 03 2017 *)

Crossrefs

Cf. A000005, A073065.

Sequence in context: A323651 A151569 A016635 * A294094 A290288 A126215

Adjacent sequences: A133989 A133990 A133991 * A133993 A133994 A133995

Keyword

nonn,easy

Author

Giovanni Teofilatto, Jan 09 2008

Extensions

Definition clarified by D. S. McNeil, Jun 28 2010

Status

approved