A190789 Numbers n such that omega(n-1) + omega(n+1) = omega(n) where omega(n) = A001221(n).

2, 6, 10, 12, 18, 24, 26, 28, 48, 66, 70, 72, 78, 80, 82, 84, 90, 108, 110, 114, 120, 130, 132, 140, 156, 170, 174, 182, 190, 192, 222, 234, 238, 242, 252, 255, 258, 264, 276, 280, 290, 294, 306, 308, 310, 318, 336, 342, 350, 354, 366, 372, 374, 378, 380, 396, 402, 408, 410, 418

Offset

1,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Formula

omega(a(n)-1) + omega(a(n)+1) = omega(a(n)).

Example

a(35)=255 because omega(254)+omega(256)=omega(255) or 2+1=3.

Mathematica

Select[Range[5000], PrimeNu[# - 1] + PrimeNu[# + 1] == PrimeNu[ #] &] (* G. C. Greubel, Apr 24 2017 *)
Flatten[Position[Partition[PrimeNu[Range[450]], 3, 1], _?(#[[1]]+#[[3]] == #[[2]]&), 1, Heads->False]]+1 (* Harvey P. Dale, Jul 31 2017 *)

Prog

(PARI) isok(n) = omega(n) == omega(n-1) + omega(n+1); \\ Michel Marcus, Apr 25 2017

Crossrefs

Cf. A001221.

Sequence in context: A357702 A263309 A253913 * A373049 A071638 A028348

Adjacent sequences: A190786 A190787 A190788 * A190790 A190791 A190792

Keyword

nonn,easy

Author

Juri-Stepan Gerasimov, May 19 2011

Extensions

a(18) corrected, a(22) added by Charles R Greathouse IV, May 24 2011

Status

approved