A281703 Numbers k such that A000005(k) = A000005(A000326(k)).

1, 2, 6, 10, 14, 18, 30, 34, 38, 46, 50, 58, 66, 78, 86, 90, 94, 98, 106, 118, 130, 134, 150, 154, 170, 174, 186, 190, 198, 206, 214, 218, 226, 234, 254, 258, 266, 270, 274, 286, 294, 310, 314, 318, 326, 338, 350, 354, 366, 370, 394, 398, 406, 410, 426, 430

Offset: 1

Author

Colin Barker, Jan 28 2017

Keywords

• nonn

Comments

Numbers k such that the number of divisors of k is equal to the number of divisors of the pentagonal number k*(3*k-1)/2.

Links

• Colin Barker, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000005, A000326, A087370, A281702.

Programs

Mathematica

Select[Range[500],DivisorSigma[0,#]==DivisorSigma[0,(#(3#-1))/2]&] (* Harvey P. Dale, Nov 12 2017 *)

PARI

select(k->numdiv(k)==numdiv(k*(3*k-1)/2), vector(500, k, k))