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

Author

Juri-Stepan Gerasimov, May 19 2011

Keywords

• nonn
• easy

Examples

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

Links

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

Crossrefs

Cf. A001221.

Programs

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 *)

PARI

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

Formula

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

Extensions

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