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
KEYWORD
nonn
AUTHOR
Charles R Greathouse IV, Jun 19 2016
STATUS
approved