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A061195
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Minimum positive numerator of s_1/1 + ... + s_n/n in lowest terms, where each s_i equals 1 or -1.
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3
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1, 1, 1, 1, 7, 1, 11, 9, 11, 11, 23, 23, 607, 251, 59, 25, 97, 97, 2647, 2647, 1337, 457, 8917, 8917, 7951, 4261, 12439, 12439, 587971, 587971, 9687661, 13828799, 505163, 1554793, 1554793, 1554793, 1526171
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OFFSET
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1,5
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LINKS
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EXAMPLE
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1/1 - 1/2 - 1/3 + 1/4 - 1/5 - 1/6 = 1/20, so a(6)=1.
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MATHEMATICA
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nMax = 19; d = {0}; Table[d = Flatten[{d + 1/n, d - 1/n}]; Min[Abs[Numerator[d]]], {n, nMax}] (* T. D. Noe, Nov 19 2013 *)
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PROG
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(PARI) a(n) = {lcmn = 1; for (i=1, n, lcmn = lcm(i, lcmn)); minn = lcmn; for (i=0, 2^(n-1)-1, b = binary(i); while (#b != n, b = concat(0, b); ); num = numerator(abs(sum(ii = 1, n, (-1)^b[ii]/ii))); minn = min(minn, num); ); return(minn); } \\ Michel Marcus, Jun 15 2013
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CROSSREFS
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Cf. A232090 (minimal possible denominator).
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KEYWORD
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nonn
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AUTHOR
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Greg Martin (gerg(AT)math.toronto.edu), Apr 19 2001
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EXTENSIONS
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STATUS
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approved
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