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 A062757 Denominator of sum of first n terms of the series 1/15 + 1/63 + 1/80 ... in which the denominators are perfect squares - 1 which are simultaneously other powers, e.g. a(1) = 15 because 16 = 4^2 = 2^4, a perfect square that is also a fourth power; hence 16-1 = 15 qualifies as a term. 2
 15, 315, 5040, 85680, 278460, 42840, 14608440, 540512280, 10810245600, 46844397600, 480155075400, 145486987846200, 17749412517236400, 5916470839078800, 10769949084069775600, 312328523438023492400 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES W. Dunham, Euler: The Master of Us All, The Mathematical Association of America, Washington D.C., 1999, p. 65. L. Euler, "Variae observationes circa series infinitas," Opera Omnia, Ser. 1, Vol. 14, pp. 216-244. LINKS EXAMPLE a(2)=63 because the perfect square 64= 8^2 = 4^3. MATHEMATICA Table[ Denominator[ Plus@@(Take[ Select[ Range[ 2, 150 ], GCD@@(Last/@FactorInteger[ # ])>1& ]^2-1, k ]^-1) ], {k, 1, 16} ] CROSSREFS Cf. A037450, A062834, A062965, A001597. Sequence in context: A133766 A289951 A112489 * A088913 A053102 A327556 Adjacent sequences:  A062754 A062755 A062756 * A062758 A062759 A062760 KEYWORD nonn AUTHOR Jason Earls, Jul 16 2001 EXTENSIONS More terms from Dean Hickerson, Jul 24, 2001 STATUS approved

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Last modified February 25 20:04 EST 2020. Contains 332258 sequences. (Running on oeis4.)