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
Keywords
Links
- Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
SequencePosition[DivisorSigma[0,Range[7600000]],{28,28}][[All,1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 10 2017 *) -
PARI
is(n)=numdiv(n)==28 && numdiv(n+1)==28
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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)