

A136155


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


5



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
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OFFSET

1,1


LINKS



FORMULA



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(n1) 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[n1] && (PrimeNu[n]==2  PrimeNu[n]==3);


CROSSREFS



KEYWORD

easy,nonn


AUTHOR



EXTENSIONS



STATUS

approved



