This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A346760 #9 Aug 03 2021 15:29:03 %S A346760 0,0,1,4,10,19,35,52,83,110,165,196,286,329,444,504,680,713,969,1016, %T A346760 1294,1375,1771,1752,2290,2314,2841,2908,3654,3476,4495,4400,5290, %U A346760 5304,6500,6124,7770,7467,8852,8688,10660,9802,12341,11700,13652,13409,16215,14768,18389,17190 %N A346760 a(n) = Sum_{d|n} mu(n/d) * binomial(d,3). %F A346760 G.f.: Sum_{k>=1} mu(k) * x^(3*k) / (1 - x^k)^4. %F A346760 a(n) = (A059376(n) - 3 * A007434(n) + 2 * A000010(n)) / 6. %t A346760 Table[Sum[MoebiusMu[n/d] Binomial[d, 3], {d, Divisors[n]}], {n, 1, 50}] %t A346760 nmax = 50; CoefficientList[Series[Sum[MoebiusMu[k] x^(3 k)/(1 - x^k)^4, {k, 1, nmax}], {x, 0, nmax}], x] // Rest %o A346760 (PARI) a(n) = sumdiv(n, d, moebius(n/d)*binomial(d, 3)); \\ _Michel Marcus_, Aug 03 2021 %Y A346760 3rd column of A020921. %Y A346760 Cf. A000010, A000292, A007434, A059376, A102309, A117108, A346761. %K A346760 nonn %O A346760 1,4 %A A346760 _Ilya Gutkovskiy_, Aug 02 2021