A331756 - OEIS

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A331756

a(n) = A306302(n)/2.

0

0, 2, 8, 23, 52, 107, 190, 324, 514, 781, 1128, 1604, 2192, 2962, 3896, 5026, 6372, 8030, 9940, 12243, 14874, 17899, 21324, 25324, 29772, 34850, 40496, 46827, 53798, 61687, 70244, 79852, 90348, 101842, 114312, 127946, 142576, 158700, 176048, 194788, 214812

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OFFSET

0,2

LINKS

Table of n, a(n) for n=0..40.

MATHEMATICA

z[n_] := Sum[If[GCD[i, j] == 1, (n-i+1)(n-j+1), 0], {i, n}, {j, n}];

a[n_] := If[n == 0, 0, (z[n] + n^2 + 2n)/2];

Table[a[n], {n, 0, 33}] (* Jean-François Alcover, Sep 14 2022 *)

CROSSREFS

Sequence in context: A161463 A190021 A014285 * A330152 A079460 A154144

Adjacent sequences: A331753 A331754 A331755 * A331757 A331758 A331759

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Feb 04 2020

STATUS

approved