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A090702
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a(n) is the minimal number k such that every binary word of length n can be transformed into a palindrome or an antipalindrome by deleting at most k letters.
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1
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0, 0, 1, 1, 1, 2, 2, 2, 3, 4, 4, 4, 5, 5, 5, 6, 7, 7, 7, 8
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,6
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COMMENTS
| A word l_0...l_n is called a palindrome if l_i=l_{n-i} for all i<=n.
A binary word l_0...l_n is called an antipalindrome if l_i<>l_{n-i} for all i<=n
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REFERENCES
| I. Protasov, Palindromial equivalence: one theorem and two problems, Matem. Studii, 14, #1, (2000), p. 111.
O. V. Ravsky, A New Measure of Asymmetry of Binary Words, Journal of Automata, Languages and Combinatorics, 8, #1 (2003), p. 75-83.
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FORMULA
| a(n)>=[(n+2*[(n-3)/7])/3] for every n and for 2<=n<=20 equality holds.
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CROSSREFS
| Cf. A090701.
Sequence in context: A006949 A194814 A055748 * A029124 A113512 A194169
Adjacent sequences: A090699 A090700 A090701 * A090703 A090704 A090705
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KEYWORD
| nonn,base
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AUTHOR
| Sasha Ravsky (oravsky(AT)mail.ru), Jan 12 2004
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