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 A191855 Second factor in happy factorization of n-th rectangular number. 7
 2, 5, 3, 10, 4, 13, 2, 17, 9, 5, 7, 11, 26, 4, 29, 6, 3, 2, 37, 19, 13, 41, 7, 4, 9, 2, 50, 13, 53, 27, 5, 8, 19, 58, 4, 61, 2, 65, 33, 17, 3, 14, 9, 73, 74, 4, 11, 3, 82, 28, 85, 43, 89, 10, 4, 31, 2, 5, 97, 2, 101, 51, 21, 106, 4, 109, 11, 37, 16, 113, 57 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) > 1; a(n) = A007967(A007969(n)) = A007969(n) / A191854(n); (A191854(n), a(n)) is a 1-happy couple; notation: C in the Conway link. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..200 J. H. Conway, On Happy Factorizations, J. Integer Sequences, Vol. 1, 1998, #1. MATHEMATICA r[b_, c_] := (red = Reduce[x > 0 && y > 0 && b*x^2 + 1 == c*y^2, {x, y}, Integers] /. C[1] -> 1 // Simplify; If[Head[red] === Or, First[red], red]); f[128] = {}(* to speed up *); f[n_] := f[n] = If[IntegerQ[Sqrt[n]], {}, Do[c = n/b; If[(r0 = r[b, c]) =!= False, {x0, y0} = {x, y} /. ToRules[r0]; Return[{b, c, x0, y0}]], {b, Divisors[n] // Most}]]; A191855 = Reap[Table[Print[n, " ", f[n]];    If[f[n] != {} && f[n] =!= Null, Sow[f[n][[2]]]], {n, 1, 130}]][[2, 1]] (* Jean-François Alcover, Sep 18 2015 *) PROG (Haskell) a191855 = a007967 . a007969  -- Reinhard Zumkeller, Oct 11 2015 CROSSREFS Cf. A007967, A007969, A191854. Sequence in context: A057337 A163233 A096666 * A064664 A323637 A349637 Adjacent sequences:  A191852 A191853 A191854 * A191856 A191857 A191858 KEYWORD nonn AUTHOR Reinhard Zumkeller, Jun 18 2011 EXTENSIONS Wrong formula removed (thanks to Wolfdieter Lang, who pointed this out) by Reinhard Zumkeller, Oct 11 2015 STATUS approved

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Last modified November 30 20:17 EST 2021. Contains 349425 sequences. (Running on oeis4.)