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A066690 Odd n such that tau(n) = tau(n+2) = 10, where tau(n) = A000005(n) is the number of divisors of n. 1
127251, 649375, 1274373, 1303047, 2206519, 2388123, 2775625, 3400623, 3585625, 3627909, 4193125, 4294375, 4311873, 5707177, 6319375, 6336873, 6926875, 7128567, 7939375, 7949581, 8101537, 11280625, 11298123, 11786875 (list; graph; refs; listen; history; text; internal format)
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: A251016 A251027 A204149 * A189185 A234978 A235318

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

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Last modified October 23 04:06 EDT 2021. Contains 348211 sequences. (Running on oeis4.)