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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

%I

%S 7,25,313,48985,1199765113,719718163185951385,

%T 258997117209879873736794713791709113,

%U 33539753361514126736178628392779244498735703225085922505721228803623385

%N a(1) = 7; for n > 1, a(n) is the hypotenuse of the right triangle with legs a(n) - 1 and a(n-1).

%C 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.

%F a(n) = (a(n-1)^2 + 1) / 2.

%e 25^2 = 24^2 + 7^2, 313^2 = 312^2 + 25^2.

%t NestList[(#^2+1)/2&,7,8]

%Y Cf. A053630 (case a(1) = 3).

%K nonn

%O 1,1

%A _Zak Seidov_, Nov 11 2013

%E b(11) = 2951438416261 (the least prime factor of a(11)) from _Jon E. Schoenfield_ and _Charles R Greathouse IV_

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Last modified August 15 15:48 EDT 2020. Contains 336504 sequences. (Running on oeis4.)