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A264748
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a(n) = Sum_{k = 1..n} (k^n - n^k).
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0
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0, -1, -3, 14, 520, 11185, 239505, 5510652, 138456936, 3803230815, 113833152565, 3695302326650, 129479186068128, 4874312730972685, 196306448145080385, 8425000059348756472, 383956514250037779376, 18521535576956405481147, 942952190208348285876501
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OFFSET
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1,3
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LINKS
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FORMULA
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a(n) = ((1 - n)*zeta(-n, n + 1) - n*(n^n - 1) + (n - 1)*zeta(-n))/(n - 1) for n>1, where zeta(s) is the Riemann zeta function and zeta(s, a) is the Hurwitz zeta function.
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EXAMPLE
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a(1) = 1^1 - 1^1 = 0;
a(2) = 1^2 - 2^1 + 2^2 - 2^2 = -1;
a(3) = 1^3 - 3^1 + 2^3 - 3^2 + 3^3 - 3^3 = -3;
a(4) = 1^4 - 4^1 + 2^4 - 4^2 + 3^4 - 4^3 + 4^4 - 4^4 = 14;
a(5) = 1^5 - 5^1 + 2^5 - 5^2 + 3^5 - 5^3 + 4^5 - 5^4 + 5^5 - 5^5 = 520, etc.
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MATHEMATICA
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Table[Sum[k^n - n^k, {k, 1, n}], {n, 1, 20}]
Join[{0}, Table[HarmonicNumber[n, -n] - n (n^n - 1)/(n - 1), {n, 2, 20}]]
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PROG
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(PARI) a(n) = sum(k=1, n, k^n - n^k); \\ Altug Alkan, Nov 23 2015
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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