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A154260
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Integers of the form : n*(4*n-+1)/2.
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4
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0, 7, 9, 30, 34, 69, 75, 124, 132, 195, 205, 282, 294, 385, 399, 504, 520, 639, 657, 790, 810, 957, 979, 1140, 1164, 1339, 1365, 1554, 1582, 1785, 1815, 2032, 2064, 2295, 2329, 2574, 2610, 2869, 2907, 3180, 3220, 3507, 3549, 3850, 3894, 4209, 4255, 4584
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also integers of the form sum(k = 1..n, k/4) = n(n+1)/8. - Alonso del Arte, Jan 20 2012
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (1,2,-2,-1,1).
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FORMULA
| A139274 UNION A139275. Conjecture: a(n)=a(n-1)+2*a(n-2)-2*a(n-3)-a(n-4)+a(n-5). G.f.: x^2*(7+2x+7x^2)/((1+x)^2*(1-x)^3). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 07 2009]
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MATHEMATICA
| Select[Union[Flatten[Table[{n (4n - 1)/2, n (4n + 1)/2}, {n, 0, 199}]]], IntegerQ] (* Alonso del Arte, Jan 20 2012 *)
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PROG
| (PARI) print1(0); forstep(n=2, 1e2, 2, print1(", "n*(4*n-1)/2", "n*(4*n+1)/2)) \\ Charles R Greathouse IV, Jan 20 2012
(PARI) print1(s=0); for(n=1, 1e3, s+=n/4; if(denominator(s)==1, print1(s", "))) \\ Charles R Greathouse IV, Jan 20 2012
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CROSSREFS
| Cf. A001318, A074378, A057569, A057570.
Sequence in context: A113124 A030404 A066930 * A186234 A085903 A200180
Adjacent sequences: A154257 A154258 A154259 * A154261 A154262 A154263
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KEYWORD
| nonn,easy
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AUTHOR
| Vladimir Orlovsky (4vladimir(AT)gmail.com), Jan 06 2009
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