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 A228047 Decimal expansion of sum of reciprocals, row 5 of the natural number array, A185787. 6
 4, 2, 3, 5, 3, 9, 0, 9, 9, 6, 0, 8, 7, 0, 0, 1, 9, 6, 8, 3, 7, 6, 0, 7, 6, 8, 9, 9, 7, 4, 4, 2, 8, 9, 3, 7, 5, 4, 4, 3, 2, 2, 8, 8, 1, 8, 9, 4, 1, 7, 1, 1, 1, 0, 2, 1, 7, 5, 6, 0, 8, 4, 2, 8, 1, 3, 0, 9, 3, 4, 7, 8, 2, 4, 5, 8, 2, 6, 7, 1, 1, 7, 8, 2, 5, 9 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Let s(n) be the sum of reciprocals of the numbers in row n of the array T at A185787 given by T(n,k) = n + (n+k-2)(n+k-1)/2, and let r = (2*pi/sqrt(7))*tanh(pi*sqrt(7)/2), as at A226985. Then s(1) = r, and s(2) to s(5) are given by A228044 to A228047. Let c(n) be the sum of reciprocals of the numbers in column n of T.  Then c(1) = 2; c(2) = 11/9, c(4) = 29/50, and c(3) is given by A228049.  Let d(n) be the sum of reciprocals of the numbers in the main diagonal, (T(n,n)); then d(2) = (1/12)*(pi)^2; d(3) = 1/2, and d(1) is given by A228048. LINKS EXAMPLE 1/15 + 1/20 + 1/26 + ... = (1/17160)(-9997 + 1760r*tanh(r)), where r = (pi/2)*sqrt(39) 1/15 + 1/20 + 1/26 + ... = 0.42353909960870019683760768997442893... MATHEMATICA \$MaxExtraPrecision = Infinity; t[n_, k_] := t[n, k] = n + (n + k - 2) (n + k - 1)/2; u = N[Sum[1/t[5, k], {k, 1, Infinity}], 130]; RealDigits[u, 10] CROSSREFS Cf. A185787, A000027, A228044, A226985. Sequence in context: A274791 A200024 A247206 * A188543 A182272 A182273 Adjacent sequences:  A228044 A228045 A228046 * A228048 A228049 A228050 KEYWORD nonn,cons,easy AUTHOR Clark Kimberling, Aug 06 2013 STATUS approved

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Last modified January 25 16:42 EST 2020. Contains 331245 sequences. (Running on oeis4.)