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A062317
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Numbers n such that 5n-1 is a perfect square.
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1
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1, 2, 10, 13, 29, 34, 58, 65, 97, 106, 146, 157, 205, 218, 274, 289, 353, 370, 442, 461, 541, 562, 650, 673, 769, 794, 898, 925, 1037, 1066, 1186, 1217, 1345, 1378, 1514, 1549, 1693, 1730, 1882, 1921, 2081, 2122, 2290, 2333, 2509, 2554, 2738, 2785, 2977
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,1000
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FORMULA
| a(n)=((2+5n)^2+1)/5 if n is odd; a(n)=((3+5n)^2+1)/5 if n is even
a(n)= +a(n-1) +2*a(n-2) -2*a(n-3) -a(n-4) +a(n-5). G.f.: x*(1+x+6*x^2+x^3+x^4)/((1+x)^2*(1-x)^3). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 30 2010]
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MATHEMATICA
| f[n_]:=IntegerQ[Sqrt[5*n-1]]; Select[Range[0, 8! ], f[ # ]&] [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Feb 19 2010]
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PROG
| (PARI) je=[]; for(n=1, 5000, if(issquare(5*n-1), je=concat(je, n))); je
(PARI) { n=0; for (m=1, 10^9, if (issquare(5*m - 1), write("b062317.txt", n++, " ", m); if (n==1000, break)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 04 2009]
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CROSSREFS
| Cf. A036666.
Sequence in context: A177856 A058216 A037386 * A140510 A098735 A050546
Adjacent sequences: A062314 A062315 A062316 * A062318 A062319 A062320
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KEYWORD
| nonn
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AUTHOR
| Santi Spadaro (spados(AT)katamail.com), Jul 12 2001
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EXTENSIONS
| More terms from Jason Earls (zevi_35711(AT)yahoo.com), Jul 14 2001
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