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%I #30 Dec 25 2016 02:44:02
%S 0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,3,0,0,0,0,3,0,0,0,0,1,0,0,0,0,0,3,
%T 0,0,0,0,6,0,0,0,0,3,0,0,0,0,0,0,0,0,0,0,3,0,0,3,0,3,0,0,6,0,0,0,0,3,
%U 0,0,0,0,0,0,0,1,0,0,6,0,0,0,0,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,3
%N Expansion of (Sum_{k>=1} x^(prime(k)^2))^3.
%C Number of ordered ways of writing n as the sum of three squares of primes (A001248).
%H <a href="/index/Su#ssq">Index entries for sequences related to sums of squares</a>
%F G.f.: (Sum_{k>=1} x^(prime(k)^2))^3.
%e a(22) = 3 because we have [4, 9, 9], [9, 4, 9] and [9, 9, 4].
%t nmax = 125; CoefficientList[Series[(Sum[x^Prime[k]^2, {k, 1, nmax}])^3, {x, 0, nmax}], x]
%Y Cf. A001248, A063691, A098238.
%K nonn
%O 0,18
%A _Ilya Gutkovskiy_, Dec 24 2016