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A213290 Number of n-length words w over binary alphabet such that for every prefix z of w we have #(z,a_i) = 0 or #(z,a_i) >= #(z,a_j) for all j>i and #(z,a_i) counts the occurrences of the i-th letter in z. 2
1, 2, 4, 5, 9, 14, 27, 46, 91, 162, 323, 589, 1177, 2179, 4357, 8152, 16303, 30746, 61491, 116689, 233377, 445095, 890189, 1704795, 3409589, 6552379, 13104757, 25258601, 50517201, 97617061, 195234121, 378098956, 756197911, 1467343306, 2934686611, 5704370761 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..1000

FORMULA

a(n) = A001405(n) + A001405(n-2) + A057427(n).

a(n) = A182172(n,2) + A182172(n-2,2) + A057427(n).

EXAMPLE

a(0) = 1: the empty word.

a(1) = 2: a, b for alphabet {a,b}.

a(2) = 4: aa, ab, ba, bb.

a(3) = 5: aaa, aab, aba, baa, bbb.

a(4) = 9: aaaa, aaab, aaba, aabb, abaa, abab, baaa, baab, bbbb.

a(5) = 14: aaaaa, aaaab, aaaba, aaabb, aabaa, aabab, aabba, abaaa, abaab, ababa, baaaa, baaab, baaba, bbbbb.

MAPLE

b:= n-> `if`(n<0, 0, binomial(n, ceil(n/2))):

a:= n-> b(n) +b(n-2) +`if`(n>0, 1, 0):

seq(a(n), n=0..40);

CROSSREFS

Column k=2 of A213276.

Cf. A001405, A057427, A182172.

Sequence in context: A077882 A234273 A120939 * A277852 A277854 A120770

Adjacent sequences:  A213287 A213288 A213289 * A213291 A213292 A213293

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Jun 08 2012

STATUS

approved

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Last modified December 7 05:14 EST 2019. Contains 329839 sequences. (Running on oeis4.)