OFFSET
0,5
COMMENTS
Number of ways to write 2n as an ordered sum of two primes with prime subscripts (A006450).
LINKS
FORMULA
G.f.: (Sum_{k>=1} x^prime(prime(k)))^2 [even terms only].
EXAMPLE
a(4) = 2 because we have [3, 5] and [5, 3], where 3 = prime(2) = prime(prime(1)) and 5 = prime(3) = prime(prime(2)).
MATHEMATICA
Take[CoefficientList[Series[Sum[x^Prime[Prime[k]], {k, 1, 250}]^2, {x, 0, 250}], x], {1, -1, 2}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jan 21 2017
STATUS
approved