A067577 a(n) = Product_{i=1..n} sigma(i) * Sum_{i=1..n} 1/sigma(i).

1, 4, 19, 145, 954, 11952, 101664, 1573344, 21179232, 390661056, 4857760512, 138055228416, 1989835352064, 48554918608896, 1184490930438144, 37179368055373824, 683493250562260992, 26913000032107757568, 548273767789158727680, 23227773590084738088960, 751700319286194622955520

Offset: 1

Author

Benoit Cloitre, Jan 30 2002

Keywords

• nonn

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..419

Crossrefs

Cf. A000203 (sigma), A066780, A212717, A212718.

Programs

Mathematica

Array[Product[DivisorSigma[1, i], {i, #}]*Sum[1/DivisorSigma[1, j], {j, #}] &, 21] (* Michael De Vlieger, Jul 16 2022 *)

PARI

a(n) = prod(i=1, n, sigma(i)) * sum(i=1, n, 1/sigma(i)); \\ Michel Marcus, Jan 09 2021

Extensions

More terms from Michel Marcus, Jan 09 2021