OFFSET
1,5
COMMENTS
The first 15 terms from this sequence and from A045917 are identical.
LINKS
Jean-François Alcover, Table of n, a(n) for n = 1..10000
Eric Weisstein's MathWorld, Chen's theorem
Wikipedia, Chen's theorem
EXAMPLE
40 = 23+17 = 29+11 = 37+3, so a(20) = 3.
Compare with 40 = 23+17 = 29+11 = 31+9 = 37+3 and A045917(20) = 4.
MATHEMATICA
a[n_] := Count[IntegerPartitions[2*n, {2}], {p_, q_} /; PrimeQ[p] && (PrimeQ[q] || Length[FactorInteger[q]] == 2)]; Table[a[n], {n, 1, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jean-François Alcover, Jan 13 2014
STATUS
approved