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A274364 Numbers n such that n and n+1 both have 28 divisors. 2
156735, 809919, 1276479, 1429568, 1649727, 1836351, 2269376, 2489535, 2549312, 2769471, 2922560, 3202496, 3236031, 4449087, 4729023, 4915647, 5068736, 5288895, 5441984, 5628608, 5721920, 6035391, 6281792, 6468416, 6595263, 6841664, 7028288, 7248447, 7528383 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

MATHEMATICA

SequencePosition[DivisorSigma[0, Range[7600000]], {28, 28}][[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 10 2017 *)

PROG

(PARI) is(n)=numdiv(n)==28 && numdiv(n+1)==28

(PARI) list(lim)=my(v=List(), t, p6); forprime(p=2, sqrtnint(lim\6, 6), p6=p^6; forprime(q=2, lim\p6\2, if(p==q, next); forprime(r=2, lim\p6\q, if(p==r || q==r, next); t=p6*q*r; if(numdiv(t+1)==28, listput(v, t)); if(numdiv(t-1)==28, listput(v, t-1))))); forprime(p=2, sqrtnint(lim\8, 6), p6=p^6; forprime(q=2, sqrtnint(lim\p6, 3), if(p==q, next); t=p6*q^3; if(numdiv(t+1)==28, listput(v, t)); if(numdiv(t-1)==28, listput(v, t-1)))); Set(v)

CROSSREFS

Intersection of A005237 and A137491.

Cf. A000005, A274357.

Sequence in context: A186605 A297060 A114658 * A258073 A245681 A278862

Adjacent sequences:  A274361 A274362 A274363 * A274365 A274366 A274367

KEYWORD

nonn

AUTHOR

Charles R Greathouse IV, Jun 19 2016

STATUS

approved

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Last modified October 16 09:29 EDT 2019. Contains 328056 sequences. (Running on oeis4.)