A175303 a(n) = number of finite sequences using numbers drawn from (1,2,3,...,n), using each number at most once, where each number in a finite sequence is not coprime to the previous number, and each finite sequence must continued if possible. (See example.)

1, 2, 3, 4, 5, 13, 14, 43, 79, 457, 458, 5145, 5146, 38237, 259920, 1702869, 1702870, 28603827, 28603828, 402599903, 3319634320, 34246343007, 34246343008

Offset

1,2

Links

Table of n, a(n) for n=1..23.

Formula

a(p)=a(p-1)+1 for all primes p.

Example

For n = 7, we have these 14 finite sequences:
1;
2,4,6,3;
2,6,3;
2,6,4;
3,6,2,4;
3,6,4,2;
4,2,6,3;
4,6,2;
4,6,3;
5;
6,2,4;
6,3;
6,4,2;
7

Crossrefs

Sequence in context: A026471 A039039 A141484 * A057158 A138986 A306294

Adjacent sequences: A175300 A175301 A175302 * A175304 A175305 A175306

Keyword

more,nonn

Author

Leroy Quet, Mar 24 2010

Extensions

More terms from Sean A. Irvine, Nov 25 2010

Status

approved