A300416 Number of prime Eisenstein integers z = x - y*w^2 with |z| <= n and where w = -1/2 + i*sqrt(3)/2 is a primitive cube root of unity.

0, 2, 4, 6, 9, 11, 15, 17, 23, 25, 30, 34, 40, 44, 50, 54, 61, 65, 71, 79, 87, 91, 98, 104, 114, 122, 128, 138, 147, 155, 161, 171, 183, 193, 199, 209, 217, 225, 237, 249, 262, 276, 286, 296, 308, 318, 331, 345, 359, 365, 377, 391, 410, 418, 428

Offset: 1

Author

Frank M Jackson and Michael B Rees, Mar 05 2018

Keywords

• nonn

Comments

Two prime Eisenstein integers are not counted separately if they are associated, i.e., if their quotient is a unit (1, -w^2, w, -1, w^2 or -w).

Examples

			a(7)=15 because the Eisenstein primes whose modulus <= 7 are 1-w^2, 1-2w^2, 1-3w^2, 1-5w^2, 1-6w^2, 2, 2-w^2, 2-3w^2, 3-w^2, 3-2w^2, 3-4w^2, 4-3w^2, 5, 5-w^2, 6-w^2.
		

Links

• Eric Weisstein's World of Mathematics, Eisenstein prime
• Wikipedia, Eisenstein integer.

Crossrefs

Cf. A055667, A062711.

Programs

Mathematica

a[n_] := Module[{w2=-1/2-I*Sqrt[3]/2, lst={}, x, y, z, Nz}, Do[z=x-w2*y; Nz=x^2+x*y+y^2; If[y==0&&Mod[Sqrt[Nz], 3]==2&&Sqrt[Nz]<=n&&PrimeQ[Sqrt[Nz]], AppendTo[lst, {x, y}], If[Mod[Nz, 3]!=2&&Sqrt[Nz]<=n&&PrimeQ[Nz], AppendTo[lst, {x, y}]]], {x, 0, n}, {y, 0, n}]; Length@lst]; Array[a, 100]