A274365 Numbers n such that n and n+1 both have 30 divisors.
180224, 257499, 579375, 1075599, 1990575, 2353616, 5598800, 10320624, 11560400, 13975983, 16951599, 17213552, 17651600, 17672499, 17784207, 20626991, 20660624, 21041775, 21912848, 22252400, 24533199, 24953103, 26161875, 26604207, 29232175, 29253392
Offset: 1
Keywords
Links
- Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
SequencePosition[Table[If[DivisorSigma[0,n]==30,1,0],{n,3*10^7}],{1,1}][[All,1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 10 2018 *) -
PARI
is(n)=numdiv(n)==30 && numdiv(n+1)==30
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PARI
list(lim)=my(v=List(),t); forprime(p=2,sqrtnint(lim\2,14), my(p14=p^14); forprime(q=2,lim\p14, if(p==q, next); t=p14*q; if(numdiv(t+1)==30, listput(v,t)); if(numdiv(t-1)==30, listput(v,t-1)))); forprime(p=2,sqrtnint(lim\4,9), my(p9=p^9); forprime(q=2,sqrtint(lim\p9), if(p==q, next); t=p9*q^2; if(numdiv(t+1)==30, listput(v,t)); if(numdiv(t-1)==30, listput(v,t-1)))); forprime(p=2,sqrtnint(lim\16,5), my(p5=p^5); forprime(q=2,sqrtnint(lim\p5,4), if(p==q, next); t=p5*q^4; if(numdiv(t+1)==30, listput(v,t)); if(numdiv(t-1)==30, listput(v,t-1)))); forprime(p=2,sqrtnint(lim\12,4), my(p4=p^4); forprime(q=2,sqrtint(lim\p4\2), if(p==q, next); my(q2=q^2); forprime(r=2,lim\p4\q2, if(p==r || q==r, next); t=p4*q2*r; if(numdiv(t+1)==30, listput(v,t)); if(numdiv(t-1)==30, listput(v,t-1))))); Set(v)