A136155 Composites one larger than a prime and with exactly two or three distinct prime factors.

6, 12, 14, 18, 20, 24, 30, 38, 42, 44, 48, 54, 60, 62, 68, 72, 74, 80, 84, 90, 98, 102, 104, 108, 110, 114, 132, 138, 140, 150, 152, 158, 164, 168, 174, 180, 182, 192, 194, 198, 200, 212, 224, 228, 230, 234, 240, 242, 252, 258, 264, 270, 272, 278, 282, 284, 294

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

Union of A136151 and A136152. Subset of A008864. - R. J. Mathar, Apr 24 2008

A136151 UNION A136152. - R. J. Mathar, May 03 2008

Example

a(1)=6, which is one larger than the prime 5 and has 2 distinct prime factors (namely 2 and 3).
60 is in the sequence because 59 is prime and 60 = 2^2*3*5 has three distinct prime factors.

Maple

A001221 := proc(n) nops(numtheory[factorset](n)) ; end: isA136155 := proc(n) if isprime(n-1) then RETURN( A001221(n)=2 or A001221(n)= 3) ; else RETURN(false) ; fi ; end: for n from 1 to 300 do if isA136155(n) then printf("%d, ", n) ; fi ; od: # R. J. Mathar, May 03 2008

Mathematica

okQ[n_] := PrimeQ[n-1] && (PrimeNu[n]==2 || PrimeNu[n]==3);
Select[Range[6, 300, 2], okQ] (* Jean-François Alcover, Feb 04 2023 *)

Crossrefs

Cf. A136151, A136152, A136153, A136154.

Sequence in context: A348251 A290648 A336549 * A315599 A136151 A315600

Adjacent sequences: A136152 A136153 A136154 * A136156 A136157 A136158

Keyword

easy,nonn

Author

Enoch Haga, Dec 16 2007

Extensions

Edited by R. J. Mathar and Jens Kruse Andersen, Apr 24 2008

Status

approved