A243220 Number of divisors of A002183(n).

1, 2, 2, 3, 4, 4, 3, 4, 6, 5, 6, 6, 8, 8, 6, 9, 8, 10, 12, 7, 12, 10, 12, 12, 12, 9, 12, 16, 8, 15, 12, 16, 18, 14, 12, 16, 12, 20, 9, 18, 14, 20, 24, 16, 15, 20, 14, 24, 24, 10, 21, 24, 16, 24, 30, 18, 18, 24, 16, 28, 30, 11, 24, 30, 18, 28, 36, 20, 21, 40, 28, 18, 32, 36, 12, 27, 36, 32, 42, 22, 48, 32, 20, 45, 36, 42, 13, 48, 30, 42, 60, 36, 48

Offset: 1

Author

N. J. A. Sloane, Jun 01 2014

Keywords

• nonn
• look

Comments

No prime number > 17 is in this sequence. - J. Lowell, Feb 06 2022

References

• S. Ramanujan, Collected Papers, Ed. G. H. Hardy et al., Cambridge 1927; Chelsea, NY, 1962, p. 87.

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000005, A002183, A002182.

Programs

Mathematica

(* This program is not suitable to compute a large number of terms. *) Reap[For[record = 0; n = 1, n <= 10^9, n = If[n < 60, n + 1, n + 60], tau = DivisorSigma[0, n]; If[tau > record, record = tau; t = DivisorSigma[0, tau]; Print[t]; Sow[t]]]][[2, 1]] (* Jean-François Alcover, Oct 08 2016 *)

Formula

a(n) = A000005(A000005(A002182(n))). - Michel Marcus, Oct 08 2016