A078664 Number of divisors of the n-th Ulam number.

1, 2, 2, 3, 4, 4, 2, 2, 5, 6, 4, 6, 9, 4, 2, 10, 2, 4, 4, 4, 12, 4, 4, 4, 2, 6, 8, 4, 8, 12, 2, 8, 4, 6, 4, 6, 4, 18, 8, 8, 2, 4, 4, 4, 4, 6, 8, 2, 6, 4, 8, 12, 8, 8, 4, 6, 4, 15, 4, 4, 6, 4, 6, 8, 4, 16, 15, 8, 2, 6, 12, 8, 2, 8, 9, 4, 16, 8, 4, 4, 4, 12, 6

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) = A000005(A002858(n)). - Amiram Eldar, Sep 29 2019

Mathematica

u = {1, 2, 3, 4, 6, 8, 11, 13, 16, 18, 26, 28, 36, 38, 47, 48, 53, 57, 62, 69, 72, 77, 82, 87, 97, 99, 102, 106, 114, 126, 131, 138, 145, 148, 155, 175, 177, 180, 182, 189, 197, 206, 209, 219, 221, 236, 238, 241, 243, 253, 258, 260, 273, 282, 309, 316, 319, 324, 339}; Table[DivisorSigma[0, u[[n]]], {n, 1, 50}]

Crossrefs

Cf. A000005, A002858.

Sequence in context: A125920 A176360 A185068 * A328388 A325954 A243503

Adjacent sequences: A078661 A078662 A078663 * A078665 A078666 A078667

Keyword

easy,nonn

Author

Joseph L. Pe, Dec 15 2002

Status

approved