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A274365 Numbers n such that n and n+1 both have 30 divisors. 2
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 (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[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 *)

PROG

(PARI) is(n)=numdiv(n)==30 && numdiv(n+1)==30

(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)

CROSSREFS

Intersection of A005237 and A137493.

Cf. A000005, A274357.

Sequence in context: A060232 A190380 A235716 * A209828 A133541 A145536

Adjacent sequences:  A274362 A274363 A274364 * A274366 A274367 A274368

KEYWORD

nonn

AUTHOR

Charles R Greathouse IV, Jun 19 2016

STATUS

approved

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Last modified October 15 17:58 EDT 2021. Contains 348033 sequences. (Running on oeis4.)