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

Author

Benoit Cloitre, Mar 04 2009

Keywords

• nonn

Comments

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

Crossrefs

Cf. A157684, A157686, A157687

Programs

PARI

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

Formula

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