A274364 Numbers n such that n and n+1 both have 28 divisors.

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

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