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A020893
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Squarefree sums of two squares.
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6
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1, 2, 5, 10, 13, 17, 26, 29, 34, 37, 41, 53, 58, 61, 65, 73, 74, 82, 85, 89, 97, 101, 106, 109, 113, 122, 130, 137, 145, 146, 149, 157, 170, 173, 178, 181, 185, 193, 194, 197, 202, 205, 218, 221, 226, 229, 233, 241, 257, 265, 269, 274, 277, 281
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Primitively but not imprimitively represented by x^2+y^2.
The disjoint union of {1}, A003654, and A031398. [From Max Alekseyev (maxale(AT)gmail.com), Mar 09 2010]
It appears that a(n) is the n-th index, k, such that f(k)=2, where f(k)=3*Sum[Floor[i^2/k],{i,1,k}] - k^2 (see A175908). [From John W. Layman (layman)AT)math.vt.edu, May 16 2011]
Squarefree numbers with no prime factors of the form 4k+3. - Franklin T. Adams-Watters, May 17 2011
Square free numbers which have all prime divisors congruent to 1 or 2 mod 4 (square free members of A202057). - Artur Jasinski, Dec 10 2011.
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LINKS
| Index entries for sequences related to sums of squares
S. R. Finch, On a Generalized Fermat-Wiles Equation
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MATHEMATICA
| lim = 17; t = Join[{1}, Select[Union[Flatten[Table[x^2 + y^2, {x, lim}, {y, x}]]], # < lim^2 && SquareFreeQ[#] &]]
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CROSSREFS
| Cf. A001481, A008784, A022544, A034023, A175908.
Sequence in context: A103215 A037942 A008784 * A145017 A003814 A031396
Adjacent sequences: A020890 A020891 A020892 * A020894 A020895 A020896
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KEYWORD
| nonn
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AUTHOR
| Steven.Finch(AT)inria.fr (S. R. Finch)
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