A331081 a(n) = Sum_{i=1..n} d_3(i)*d_3(i+1)/3, where d_3(n) = A007425(n).

1, 4, 10, 16, 25, 34, 44, 64, 82, 91, 109, 127, 136, 163, 208, 223, 241, 259, 277, 331, 358, 367, 397, 457, 475, 505, 565, 583, 610, 637, 658, 721, 748, 775, 883, 919, 928, 955, 1045, 1075, 1102, 1129, 1147, 1255, 1309, 1318, 1363, 1453, 1489, 1543, 1597, 1615, 1645, 1735, 1825, 1915, 1942, 1951, 2005, 2059

Offset

1,2

Comments

For background references see A330570.

Links

Seiichi Manyama, Table of n, a(n) for n = 1..10000

Formula

a(n) = A331080(n) / 3. - Amiram Eldar, Apr 19 2024

Mathematica

f[p_, e_] := (e+1)*(e+2)/2;  s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; With[{t = Array[s, 100]}, Accumulate[Most[t] * Rest[t]] / 3] (* Amiram Eldar, Apr 19 2024 *)

Crossrefs

Cf. A007425, A331080.

Sequence in context: A322948 A277368 A067274 * A054901 A019574 A095273

Adjacent sequences: A331078 A331079 A331080 * A331082 A331083 A331084

Keyword

nonn

Author

N. J. A. Sloane, Jan 10 2020

Status

approved