

A156351


a(n)=sum_{k=1..n} (1)^K(k+1)*(K(k+1)K(k)) where K(k)=A000002(k)


1



1, 1, 2, 2, 3, 4, 5, 5, 6, 7, 7, 8, 8, 9, 10, 10, 11, 11, 12, 13, 14, 14, 15, 16, 17, 17, 18, 18, 19, 20, 20, 21, 22, 23, 23, 24, 25, 25, 26, 26, 27, 28, 29, 29, 30, 31, 32, 32, 33, 34, 34, 35, 35, 36, 37, 37, 38, 38, 39, 40, 41, 41, 42, 43, 43, 44, 44, 45, 46, 46, 47, 48, 49, 49
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OFFSET

1,3


COMMENTS

a(n)=1 plus the number of symbol changes in the first n terms of A078880. [From JeanMarc Fedou and Gabriele Fici, Mar 18 2010]


LINKS

Table of n, a(n) for n=1..74.
J.M. Fedou and G. Fici, Some remarks on differentiable sequences and recursivity, Journal of Integer Sequences 13(3): Article 10.3.2 (2010). [From JeanMarc Fedou and Gabriele Fici, Mar 18 2010]


FORMULA

nA054353(a(n))=1 if n is in A078649, nA054353(a(n))=0 otherwise. A078649(n+1a(n))n takes values among {0,1,2,3}.


MATHEMATICA

a2 = {1, 2, 2}; Do[ a2 = Join[a2, {1 + Mod[n  1, 2]}], {n, 3, 80}, {i, 1, a2[[n]]}]; a[n_] := Sum[(1)^a2[[k + 1]]*(a2[[k + 1]]  a2[[k]]), {k, 1, n}]; Table[a[n], {n, 1, 80}] (* JeanFrançois Alcover, Jun 18 2013 *)


CROSSREFS

Sequence in context: A242976 A218445 A034137 * A057561 A064726 A274616
Adjacent sequences: A156348 A156349 A156350 * A156352 A156353 A156354


KEYWORD

nonn


AUTHOR

Benoit Cloitre, Feb 08 2009


STATUS

approved



