A190355 Numbers n such that d(n-1)=d(n+1)=12 where d(k)=A000005(k) (number of divisors of k).

199, 307, 341, 349, 351, 415, 491, 737, 739, 851, 949, 1013, 1061, 1149, 1205, 1211, 1275, 1277, 1313, 1315, 1421, 1667, 1695, 1747, 1925, 2049, 2149, 2276, 2357, 2365, 2683, 2717, 2827, 2889, 2891, 2949, 3051, 3115, 3173, 3259, 3475, 3581, 3651, 3797, 4013, 4045, 4149, 4193, 4449, 4597, 4627, 4654, 4843

Offset: 1

Author

Juri-Stepan Gerasimov, May 09 2011

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A189974, A190267.

Programs

Mathematica

Select[Range[2, 8000], DivisorSigma[0, # - 1] == 12 && DivisorSigma[0, # + 1] == 12 &] (* G. C. Greubel, Dec 29 2017 *)
SequencePosition[DivisorSigma[0,Range[5000]],{12,,12}][[All,1]]+1 (* _Harvey P. Dale, Jul 21 2021 *)

PARI

for(n=2,10^4,if( numdiv(n-1)==12 && numdiv(n+1)==12, print1(n,", "))); /* Joerg Arndt, May 13 2011 */

Formula

A000005(a(n)-1) = A000005(a(n)+1) = 12.

Extensions

Terms corrected by R. J. Mathar, May 25 2011