A157684 a(n)=#{1<=k<=n : [K(k),K(k+1)]=[1,2]} where K=A000002

1, 1, 1, 1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 7, 8, 8, 9, 9, 9, 9, 10, 10, 10, 11, 11, 12, 12, 12, 13, 13, 13, 13, 14, 14, 15, 15, 15, 16, 16, 16, 17, 17, 17, 18, 18, 18, 19, 19, 19, 19, 20, 20, 21, 21, 21, 22, 22, 22, 22, 23, 23, 23, 24, 24, 25, 25, 25, 26, 26, 26, 27

Offset

1,5

Comments

Presumably a(n)=n/3+o(n)

Links

Table of n, a(n) for n=1..79.

Formula

a(n)=sum(k=1,n,(K(k+1)-1)*(K(k+1)-K(k))) where K(k)=A000002(k).

Prog

(PARI) a(n)=sum(k=1, n, if(abs(A000002(k)-1)+abs(A000002(k+1)-2), 0, 1))

Crossrefs

Cf. A157685, A157686, A157687

Sequence in context: A194327 A058032 A056155 * A194339 A194335 A026099

Adjacent sequences: A157681 A157682 A157683 * A157685 A157686 A157687

Keyword

nonn

Author

Benoit Cloitre, Mar 04 2009

Status

approved