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

1,1

Links

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

Formula

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

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 *)

Prog

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

Crossrefs

Cf. A189974, A190267.

Sequence in context: A142232 A166459 A304368 * A213078 A142682 A088294

Adjacent sequences: A190352 A190353 A190354 * A190356 A190357 A190358

Keyword

nonn

Author

Juri-Stepan Gerasimov, May 09 2011

Extensions

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

Status

approved