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A066692
Odd numbers k such that tau(k) = tau(k+2), where tau(k) = A000005(k) is the number of divisors of k.
2
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
Sequence in context: A286264 A347027 A147350 * A123533 A144105 A141262
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