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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
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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
Table of n, a(n) for n=1..8.
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
*
A364644
A197721
A261421
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 April 24 22:17 EDT 2024. Contains 371964 sequences. (Running on oeis4.)