OFFSET
1,10
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
Mathematics StackExchange, A question regarding the amount of composite solutions for a equation
EXAMPLE
a(10) = 2 because there are two k such that k and 10-k are composite, namely 4 and 6.
MAPLE
f:= proc(x) nops(select(t -> not isprime(t) and not isprime(x-t), [$2..x-2])) end proc:
map(f, [$1..100]);
MATHEMATICA
a[n_] := Count[Range[4, n - 4], x_ /; CompositeQ[x] && CompositeQ[n - x]]; Array[a, 90] (* Giovanni Resta, Jan 23 2020 *)
PROG
(Magma) [#[k: k in [2..n-2] | not IsPrime(k) and not IsPrime(n-k)]: n in [1..81]]; // Marius A. Burtea, Jan 22 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Jan 22 2020
STATUS
approved