A133992 - OEIS

%I #9 Feb 03 2017 17:50:10

%S 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,

%T 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,

%U 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

%N a(n) = tau( prime(n)*prime(prime(n)) - 1 ).

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

%p 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

%t Table[DivisorSigma[0, Prime[n]*Prime[Prime[n]] - 1], {n, 100}] (* _Wesley Ivan Hurt_, Feb 03 2017 *)

%Y Cf. A000005, A073065.

%K nonn,easy

%O 1,1

%A _Giovanni Teofilatto_, Jan 09 2008

%E Definition clarified by _D. S. McNeil_, Jun 28 2010