A141115 Those positive integers k where both d(d(k)) is not coprime to k and d(d(k)) does not divide k, where d(k) is the number of divisors of k.

18, 30, 42, 50, 54, 66, 70, 78, 98, 102, 110, 114, 130, 138, 140, 154, 160, 162, 170, 174, 182, 186, 190, 200, 220, 222, 224, 230, 238, 242, 246, 250, 258, 260, 266, 282, 286, 290, 308, 310, 315, 318, 322, 338, 340, 350, 352, 354, 364, 366, 370, 374, 380, 392

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

50 has 6 divisors and 6 has 4 divisors. 4 is not coprime to 50 and 4 does not divide 50. So 50 is in the sequence.

Mathematica

Select[Range[400], GCD[DivisorSigma[0, DivisorSigma[0, # ]], # ] > 1 && Mod[ #, DivisorSigma[0, DivisorSigma[0, # ]]] > 0 &] (* Stefan Steinerberger, Jun 05 2008 *)

Crossrefs

Cf. A010553, A141113, A141114.

Sequence in context: A154367 A161164 A092357 * A039320 A043143 A043923

Adjacent sequences: A141112 A141113 A141114 * A141116 A141117 A141118

Keyword

nonn

Author

Leroy Quet, Jun 04 2008

Extensions

More terms from Stefan Steinerberger, Jun 05 2008

Status

approved