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A157684 a(n)=#{1<=k<=n : [K(k),K(k+1)]=[1,2]} where K=A000002 3
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 21 17:37 EDT 2021. Contains 348155 sequences. (Running on oeis4.)