A066690 Odd n such that tau(n) = tau(n+2) = 10, where tau(n) = A000005(n) is the number of divisors of n.

127251, 649375, 1274373, 1303047, 2206519, 2388123, 2775625, 3400623, 3585625, 3627909, 4193125, 4294375, 4311873, 5707177, 6319375, 6336873, 6926875, 7128567, 7939375, 7949581, 8101537, 11280625, 11298123, 11786875

Offset

1,1

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Mathematica

Do[ If[ DivisorSigma[0, 2n - 1] == DivisorSigma[0, 2n + 1] == 10, Print[2n - 1]], {n, 1, 10^7} ]
2*SequencePosition[Table[If[DivisorSigma[0, n]==10, 1, 0], {n, 1, 11786879, 2}], {1, 1}][[All, 1]]-1 (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 14 2019 *)

Prog

(PARI) for (n=1, 2000000, if ((numdiv(2*n-1)==10) && (numdiv(2*n+1)==10), write("tau=tau=10.txt", 2*n-1, "::", tau(2*n-1))))
(PARI) { n=0; for (m=1, 10^10, if ((numdiv(2*m-1)==10) && (numdiv(2*m+1)==10), write("b066690.txt", n++, " ", 2*m-1); if (n==1000, return)) ) } \\ Harry J. Smith, Mar 17 2010

Crossrefs

Sequence in context: A349284 A251027 A204149 * A189185 A349698 A234978

Adjacent sequences: A066687 A066688 A066689 * A066691 A066692 A066693

Keyword

nonn

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 17 2010

Status

approved