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

Offset: 1

Author

Reinhard Zumkeller, Apr 08 2006

Keywords

• nonn

Comments

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

Examples

			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

Cf. A018805.