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A097268
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Numbers that are both the sum of two nonzero squares and the difference of two nonzero squares.
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22
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5, 8, 13, 17, 20, 25, 29, 32, 37, 40, 41, 45, 52, 53, 61, 65, 68, 72, 73, 80, 85, 89, 97, 100, 101, 104, 109, 113, 116, 117, 125, 128, 136, 137, 145, 148, 149, 153, 157, 160, 164, 169, 173, 180, 181, 185, 193, 197, 200, 205, 208, 212, 221, 225, 229, 232, 233
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Intersection of A000404 (sum of squares) and A024352 (difference of squares).
Also: Numbers of the form x^2+4y^2, where x and y are positive integers. Cf. A154777, A092572, A154778 for analogous sequences. [From M. F. Hasler (www.univ-ag.fr/~mhasler), Jan 24 2009]
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LINKS
| Eric Weisstein's World of Mathematics, Sum of Squares Function.
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PROG
| (PARI) isA097268(n) = forstep( b=2, sqrtint(n-1), 2, issquare(n-b^2) & return(1)) [From M. F. Hasler (www.univ-ag.fr/~mhasler), Jan 24 2009]
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CROSSREFS
| Cf. A000404, A024352, A097269-A097271.
Sequence in context: A047615 A140488 A058240 * A003653 A003655 A082823
Adjacent sequences: A097265 A097266 A097267 * A097269 A097270 A097271
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KEYWORD
| nonn
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AUTHOR
| Ray Chandler (rayjchandler(AT)sbcglobal.net), Aug 19 2004
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