A086417 Sum of divisors of 3-smooth numbers.

1, 3, 4, 7, 12, 15, 13, 28, 31, 39, 60, 40, 63, 91, 124, 120, 127, 195, 121, 252, 280, 255, 403, 363, 508, 600, 364, 511, 819, 847, 1020, 1240, 1092, 1023, 1651, 1815, 1093, 2044, 2520, 2548, 2047, 3315, 3751, 3279, 4092, 5080, 5460, 4095, 3280

Offset

1,2

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Formula

a(n) = A000203(A003586(n));

a(n) = (2^(A022328(n)+1)-1)*(3^(A022329(n)+1)-1)/2.

a(n) = A000225(j) * A003462(k) for some j,k > 0. - Flávio V. Fernandes, May 29 2021

Mathematica

DivisorSigma[1, #]&/@Select[Range[4000], Max[FactorInteger[#][[All, 1]]]<4&] (* Harvey P. Dale, Feb 14 2017 *)

Prog

(Haskell)
a086417 n = (2 ^ (a022328 n + 1) - 1) * (3 ^ (a022329 n + 1) - 1) `div` 2
-- Reinhard Zumkeller, Nov 19 2015

Crossrefs

Cf. A086416.

Cf. A000203, A003586, A022328, A022329.

Sequence in context: A305185 A083561 A018195 * A051215 A192112 A034885

Adjacent sequences: A086414 A086415 A086416 * A086418 A086419 A086420

Keyword

nonn

Author

Reinhard Zumkeller, Jul 18 2003

Status

approved