A129927 3-almost prime octagonal numbers.

8, 645, 833, 1045, 1281, 1825, 2465, 2821, 3201, 3605, 4961, 7701, 8965, 12545, 15841, 17633, 18565, 20501, 23585, 24661, 25761, 26885, 28033, 30401, 34133, 36741, 45141, 51221, 52801, 57685, 59361, 62785, 66305, 68101, 71765, 73633

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Formula

A000567 INTERSECT A014612. - R. J. Mathar, Jan 27 2009

Maple

A000567 := proc(n) n*(3*n-2) ; end: isA014612 := proc(n) RETURN( numtheory[bigomega](n) = 3) ; end: for n from 1 to 300 do q := A000567(n) ; if isA014612(q) then printf("%d, ", q) ; fi; od: # R. J. Mathar, Jan 27 2009

Mathematica

Select[Table[n(3n-2), {n, 200}], PrimeOmega[#]==3&] (* Harvey P. Dale, May 31 2016 *)

Prog

(PARI) issemi(n)=bigomega(n)==2
list(lim)=my(v=List(), t, n=1); while((t=n*(3*n-2))<=lim, if((isprime(n) && issemi(3*n-2)) || (isprime(3*n-2) && issemi(n)), listput(v, t)); n++); Vec(v) \\ Charles R Greathouse IV, Feb 05 2017

Crossrefs

Sequence in context: A083942 A274588 A027877 * A196800 A196588 A197045

Adjacent sequences: A129924 A129925 A129926 * A129928 A129929 A129930

Keyword

nonn

Author

Giovanni Teofilatto, Jun 06 2007

Extensions

Corrected and extended by R. J. Mathar, Jan 27 2009

Status

approved