A033858 Numbers k such that j(k) + ud(k) = d(k), where j(k) = A033831, ud(k) = number of unitary divisors of k (A034444), d(k) = number of divisors of k (A000005).

1, 2, 4, 8, 9, 12, 20, 24, 25, 27, 40, 49, 54, 88, 104, 120, 121, 125, 135, 136, 152, 168, 169, 184, 189, 232, 248, 250, 264, 270, 280, 289, 296, 297, 312, 328, 343, 344, 351, 361, 375, 376, 378, 408, 424, 440, 456, 459, 472, 488, 513, 520, 529, 536, 568, 584

Offset: 1

Author

Naohiro Nomoto

Keywords

• easy
• nonn

Links

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

Crossrefs

Cf. A000005, A033831, A034444.

Programs

Mathematica

j[n_] := DivisorSum[n, 1&, # > 2 && n/# < #-1 &]; Select[Range[10^3], j[#] + 2^PrimeNu[#] == DivisorSigma[0, #] &] (* Amiram Eldar, Jul 14 2019 *)

Extensions

More terms from Amiram Eldar, Jul 14 2019