A331080 - OEIS

A331080

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

3, 12, 30, 48, 75, 102, 132, 192, 246, 273, 327, 381, 408, 489, 624, 669, 723, 777, 831, 993, 1074, 1101, 1191, 1371, 1425, 1515, 1695, 1749, 1830, 1911, 1974, 2163, 2244, 2325, 2649, 2757, 2784, 2865, 3135, 3225, 3306, 3387, 3441, 3765, 3927, 3954, 4089, 4359, 4467, 4629, 4791, 4845, 4935, 5205, 5475

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OFFSET

1,1

COMMENTS

For background references see A330570.

LINKS

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

FORMULA

a(n) = 3 * A331081(n). - 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]]] (* Amiram Eldar, Apr 19 2024 *)

CROSSREFS

Cf. A007425, A331081, A331130.

Sequence in context: A199035 A101459 A051408 * A164013 A057671 A027480

Adjacent sequences: A331077 A331078 A331079 * A331081 A331082 A331083

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jan 10 2020

STATUS

approved