A331243 a(n) = number of triangles with integer sides i <= j <= k with diameter of enclosing circle <= n.
0, 1, 4, 8, 16, 26, 39, 56, 79, 106, 138, 175, 221, 272, 331, 397, 471, 555, 648, 750
Offset: 1
Examples
The sorted list of diameters D(n), rounded to 10^-4, starts: {1.1547, 2.0656, 2.3094, 3.0000, 3.0426, 3.1820, 3.4641, 4.0000, 4.0249, 4.0316, 4.1312, 4.3149, 4.6188, 5.0000, 5.0000, 5.0000, 5.0252, ...}.
a(1) = 0: 0 circles with D <= 1,
a(2) = 1: 1 circle (D = 1.1547) with 1 < D <= 2,
a(3) = 4: a(2) + 3 circles (D = 2.0656, 2.3094, 3.0000) with 2 < D <= 3,
a(4) = 8: a(3) + 4 circles (D = 3.04, 3.18, 3.46, 4.00) with 3 < D <= 4,
a(5) = 16: a(4) + 8 circles (D = 4.0249, ..., 5, 5, 5) with 4 < D <= 5.
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