OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
33 = 3*11 is a semiprime, and cannot be represented as twice a prime plus three times a prime. 21=3*7 is a semiprime which CAN be represented in that form, i.e. 2*3+3*5, and thus is not in this sequence.
MAPLE
N:= 10^4: # to get all terms <= N
Primes:= select(isprime, [2, seq(i, i=3..N/2, 2)]):
Cands:= {seq(i, i=1..N, 2)} minus {seq(seq(2*p+3*q, p=Primes), q=Primes)}:
sort(convert(select(numtheory:-bigomega=2, Cands), list)); # Robert Israel, Jan 09 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Randy L. Ekl, Jan 02 2017
STATUS
approved