A117991 - OEIS

A117991

Number of distinct rational numbers that can be written as fractions of the first n composite numbers.

1, 3, 7, 11, 19, 23, 35, 41, 53, 59, 67, 77, 101, 109, 131, 161, 179, 197, 205, 227, 247, 289, 317, 333, 381, 407, 431, 445, 473, 495, 555, 575, 629, 657, 693, 729, 751, 801, 835, 877, 957, 975, 1059, 1097, 1147, 1209, 1235, 1283, 1335, 1367, 1397, 1499, 1539

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OFFSET

1,2

COMMENTS

a(n) = 2*A117992(n) + 1.

LINKS

Table of n, a(n) for n=1..53.

EXAMPLE

n=3, the first 3 composite numbers are 4,6 and 8:

a(3) = #{4/4, 4/6, 4/8, 6/4, 6/6, 6/8, 8/4, 8/6, 8/8} =

= #{1/2, 2/3, 3/4, 1/1, 4/3, 3/2, 2/1} = 7.

CROSSREFS