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 A231579 a(1) = 7; for n > 1, a(n) is the hypotenuse of the right triangle with legs a(n) - 1 and a(n-1). 0
 7, 25, 313, 48985, 1199765113, 719718163185951385, 258997117209879873736794713791709113, 33539753361514126736178628392779244498735703225085922505721228803623385 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Least prime factors of a(n): 7, 5, 313, 5, 1199765113, 5, 233, 5, 101, 5, 2951438416261, 5, 457, 5, 373, 5, 89, 5, 101, 5. LINKS FORMULA a(n) = (a(n-1)^2 + 1) / 2. EXAMPLE 25^2 = 24^2 + 7^2, 313^2 = 312^2 + 25^2. MATHEMATICA NestList[(#^2+1)/2&, 7, 8] CROSSREFS Cf. A053630 (case a(1) = 3). Sequence in context: A290882 A197651 A198022 * A197721 A261421 A081298 Adjacent sequences:  A231576 A231577 A231578 * A231580 A231581 A231582 KEYWORD nonn AUTHOR Zak Seidov, Nov 11 2013 EXTENSIONS b(11) = 2951438416261 (the least prime factor of a(11)) from Jon E. Schoenfield and Charles R Greathouse IV STATUS approved

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Last modified August 5 21:18 EDT 2020. Contains 336213 sequences. (Running on oeis4.)