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A327878
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Irregular triangle read by rows: T(n,k) is the number of primitive (period n) periodic palindromes using exactly k different symbols, 1 <= k <= 1 + floor(n/2).
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8
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1, 0, 1, 0, 2, 0, 3, 3, 0, 6, 6, 0, 7, 21, 12, 0, 14, 36, 24, 0, 18, 90, 132, 60, 0, 28, 150, 240, 120, 0, 39, 339, 900, 960, 360, 0, 62, 540, 1560, 1800, 720, 0, 81, 1149, 4968, 9300, 7920, 2520, 0, 126, 1806, 8400, 16800, 15120, 5040, 0, 175, 3765, 24588, 71400, 103320, 73080, 20160
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OFFSET
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1,5
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COMMENTS
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Primitive periodic palindromes may also be called achiral Lyndon words.
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LINKS
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FORMULA
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T(n,k) = Sum_{j=1..k} (-1)^(k-j)*binomial(k,j)*A284856(n,j).
Column k is the Moebius transform of column k of A305540.
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EXAMPLE
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Triangle begins:
1;
0, 1;
0, 2;
0, 3, 3;
0, 6, 6;
0, 7, 21, 12;
0, 14, 36, 24;
0, 18, 90, 132, 60;
0, 28, 150, 240, 120;
0, 39, 339, 900, 960, 360;
0, 62, 540, 1560, 1800, 720;
0, 81, 1149, 4968, 9300, 7920, 2520;
0, 126, 1806, 8400, 16800, 15120, 5040;
0, 175, 3765, 24588, 71400, 103320, 73080, 20160;
...
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PROG
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(PARI) T(n, k) = {sumdiv(n, d, moebius(n/d) * k! * (stirling((d+1)\2, k, 2) + stirling(d\2+1, k, 2)))/2}
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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