A066692 Odd numbers k such that tau(k) = tau(k+2), where tau(k) = A000005(k) is the number of divisors of k.

3, 5, 11, 17, 29, 33, 41, 55, 59, 71, 85, 91, 93, 101, 107, 123, 137, 141, 143, 149, 159, 179, 183, 185, 191, 197, 201, 203, 213, 215, 217, 219, 227, 235, 239, 243, 247, 265, 269, 281, 299, 301, 303, 311, 319, 321, 327, 339, 341, 347, 391, 393, 411, 413, 415

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harry J. Smith)

Formula

a(n) = 2*A190276(n) - 1. - Amiram Eldar, Dec 02 2023

Mathematica

d[n_] := d[n] = DivisorSigma[0, n]; Select[Range[1, 420, 2], d[#] == d[# + 2] &] (* Amiram Eldar, Dec 02 2023 *)

Prog

(PARI) for (n=2, 1000, if (numdiv(2*n-1)==numdiv(2*n+1), print1(2*n-1, ", ")))
(PARI) { n=0; for (m=2, 10^10, if (numdiv(2*m-1) == numdiv(2*m+1), write("b066692.txt", n++, " ", 2*m-1); if (n==1000, return)) ) } \\ Harry J. Smith, Mar 18 2010

Crossrefs

Cf. A000005, A190276.

Sequence in context: A286264 A347027 A147350 * A123533 A144105 A141262

Adjacent sequences: A066689 A066690 A066691 * A066693 A066694 A066695

Keyword

nonn,easy

Author

Jon Perry, Jan 11 2002

Extensions

Edited by Dean Hickerson, Jan 13 2002

Offset changed from 0 to 1 by Harry J. Smith, Mar 18 2010

Status

approved