A069062 Numbers k such that k^2-1 and k^2+1 have the same number of positive divisors.

2, 3, 12, 30, 42, 60, 68, 102, 108, 112, 123, 128, 162, 168, 198, 200, 212, 213, 252, 294, 302, 312, 318, 333, 336, 338, 372, 387, 447, 448, 450, 462, 498, 502, 522, 542, 578, 592, 598, 600, 606, 612, 648, 672, 678, 708, 717, 752, 762, 795, 808, 810, 812

Offset: 1

Author

Benoit Cloitre, Apr 04 2002

Keywords

• easy
• nonn

Links

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

Crossrefs

Cf. A000005, A002522, A005563, A193432, A347191.

Programs

Mathematica

Select[Range[1000], DivisorSigma[0, #^2 - 1] == DivisorSigma[0, #^2 + 1] &] (* Amiram Eldar, Jun 04 2022 *)

PARI

isok(n) = numdiv(n^2-1) == numdiv(n^2+1); \\ Michel Marcus, Nov 24 2013