A157685 a(n)=#{1<=k<=n : [K(k),K(k+1)]=[2,1]} where K=A000002

0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 5, 6, 6, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12, 13, 13, 13, 14, 14, 14, 15, 15, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 19, 19, 19, 20, 20, 20, 21, 21, 21, 22, 22, 22, 23, 23, 23, 24, 24, 24, 25, 25, 26, 26, 26

Offset

1,6

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

Prog

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

Crossrefs

Cf. A157684, A157686, A157687

Sequence in context: A099741 A047743 A062299 * A220658 A127757 A172264

Adjacent sequences: A157682 A157683 A157684 * A157686 A157687 A157688

Keyword

nonn

Author

Benoit Cloitre, Mar 04 2009

Status

approved