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A078651 Number of geometric subsequences of [1,...,n] with integral successive-term ratio and length >= 1. 1
1, 3, 5, 9, 11, 15, 17, 23, 27, 31, 33, 40, 42, 46, 50, 59, 61, 68, 70, 77, 81, 85, 87, 97, 101, 105, 111, 118, 120, 128, 130, 141, 145, 149, 153, 165, 167, 171, 175, 185, 187, 195, 197, 204, 211, 215, 217, 231, 235, 242, 246, 253, 255, 265, 269, 279, 283, 287 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The number of geometric subsequences of [1,...,n] with integral successive-term ratio r and length k is floor(n/r^(k-1))(n > 0, r > 1, k > 0).

LINKS

Table of n, a(n) for n=1..58.

FORMULA

a(n) = n + sum {r > 1, j > 0} floor(n/r^j)

EXAMPLE

a(1): [1]; a(2): [1],[2],[1,2]; a(3): [1],[2],[3],[1,2],[1,3]

CROSSREFS

a(n) = n + A078632(n).

Sequence in context: A268174 A166104 A164121 * A268732 A101114 A120696

Adjacent sequences:  A078648 A078649 A078650 * A078652 A078653 A078654

KEYWORD

nonn,easy

AUTHOR

Robert E. Sawyer (rs.1(AT)mindspring.com), Jan 08, 2003

STATUS

approved

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Last modified November 14 12:44 EST 2019. Contains 329116 sequences. (Running on oeis4.)