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a(n) = number of Eisenstein primes (see A055664) of norm <= n.
4

%I #13 Feb 28 2018 08:09:52

%S 0,0,0,6,12,12,12,24,24,24,24,24,24,36,36,36,36,36,36,48,48,48,48,48,

%T 48,54,54,54,54,54,54,66,66,66,66,66,66,78,78,78,78,78,78,90,90,90,90,

%U 90,90,90,90,90,90,90,90,90,90,90,90,90,90,102,102,102,102,102

%N a(n) = number of Eisenstein primes (see A055664) of norm <= n.

%D L. W. Reid, The Elements of the Theory of Algebraic Numbers, MacMillan, NY, 1910, see Chap. VI.

%F a(n) = a(n-1) + A055667(n) for n > 0. - _Seiichi Manyama_, Dec 09 2017

%t A055667[n_] := Which[n == 3, 6, PrimeQ[n] && Mod[n, 6] == 1, 12, PrimeQ[p = Sqrt[n]] && Mod[p, 3] == 2, 6, True, 0]; Accumulate[Array[A055667, 66, 0]] (* _Jean-François Alcover_, Feb 28 2018 *)

%Y Cf. A135461, A055664, A055667.

%K nonn

%O 0,4

%A _N. J. A. Sloane_, Feb 06 2008

%E Terms corrected by _Seiichi Manyama_, Dec 09 2017