A072688 Of the first n integers (inclusive), how many of them have a prime number of letters in their English names?

1, 2, 3, 3, 3, 4, 5, 6, 6, 7, 7, 7, 7, 7, 8, 9, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 12, 13, 13, 13, 13, 13, 14, 14, 14, 14, 15, 16, 16, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 20

Offset

1,2

Links

Table of n, a(n) for n=1..70.

Formula

a(n)=number of terms of A072685 <= n.

Example

Sequence A072685 begins: 1, 2, 3, 6, 7, 8, 10 so there are 3 terms up to and including n=4, 3 terms up to and including n=5, 6 terms up to and including n=9. Therefore a(4)=3, a(5)=3, a(9)=6.

Crossrefs

Cf. A072685, A072687.

Sequence in context: A037458 A296816 A064474 * A120504 A025772 A211535

Adjacent sequences: A072685 A072686 A072687 * A072689 A072690 A072691

Keyword

easy,nonn,word

Author

Mark Hudson (mrmarkhudson(AT)hotmail.com), Jul 02 2002

Status

approved