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A078664 Number of divisors of the n-th Ulam number. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified July 4 18:38 EDT 2020. Contains 335448 sequences. (Running on oeis4.)