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A156840
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Numbers n > 1 such that n^2 == 1 (mod 900).
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3
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199, 251, 449, 451, 649, 701, 899, 901, 1099, 1151, 1349, 1351, 1549, 1601, 1799, 1801, 1999, 2051, 2249, 2251, 2449, 2501, 2699, 2701, 2899, 2951, 3149, 3151, 3349, 3401, 3599, 3601, 3799, 3851, 4049, 4051, 4249, 4301, 4499, 4501, 4699, 4751, 4949, 4951
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Numbers n such that n is +-1 mod 4, 9, and 25. [Charles R Greathouse IV, Dec 23 2011]
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index to sequences with linear recurrences with constant coefficients, signature (1,0,0,1,-1).
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FORMULA
| a(n)=a(n-1)+a(n-4)-a(n-5). [R. J. Mathar, Aug 18 2009]
Contribution from Jon E. Schoenfield (jonscho(AT)hiwaay.net), Jun 19 2010: (Start)
a(n)=(2*n+1)*225/4+f(n mod 4)/4 where f(0)=-221, f(1)=121, f(2)=-121, f(3)=221,
so a nonrecursive formula for a(n) is
a(n)=(450*n+225-(100*Floor(((n-1) mod 4)/2)+121)*(-1)^n)/4. (End)
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MATHEMATICA
| LinearRecurrence[{1, 0, 0, 1, -1}, {199, 251, 449, 451, 649}, 50] (* From Harvey P. Dale, Apr 29 2011 *)
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PROG
| (PARI) a(n)=n\8*900+[1, 199, 251, 449, 451, 649, 701, 899][n%8+1] \\ Charles R Greathouse IV, Dec 23 2011
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CROSSREFS
| Sequence in context: A109561 A031930 A160342 * A142232 A166459 A190355
Adjacent sequences: A156837 A156838 A156839 * A156841 A156842 A156843
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KEYWORD
| nonn,easy,changed
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AUTHOR
| Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Feb 17 2009
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EXTENSIONS
| Edited and a(11) corrected by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 18 2009
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