OFFSET
1,2
COMMENTS
Arises in Goldbach conjecture.
FORMULA
EXAMPLE
1 is a term because there is a unique decomposition of 2*1 = 2 into a sum of two primes (counting 1 as a prime), namely 2 = 1 + 1.
12 is a term because there are 4 decompositions of 2*12 = 24 into a sum of two primes (counting 1 as a prime), namely 1 + 23, 5 + 19, 7 + 17, and 11 + 13, and 4 is a composite number.
PROG
(Sage)
def is_A188766(n):
pp = set(prime_range(2*n+1)+[1])
return not is_prime(len([x for x in Partitions(2*n, length=2) if set(x) <= pp]))
# D. S. McNeil, Apr 10 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Apr 09 2011
STATUS
approved