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2, 2, 3, 5, 8, 12, 17, 23, 30, 38, 47, 57, 68, 80, 93, 107, 122, 138, 155, 173, 192, 212, 233, 255, 278, 302, 327, 353, 380, 408, 437, 467, 498, 530, 563, 597, 632, 668, 705, 743, 782, 822, 863, 905, 948, 992, 1037, 1083, 1130, 1178, 1227, 1277, 1328, 1380
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| a(1) = 2; then add 0 to the first number, then 1, 2, 3, 4... and so on.
Essentially the same as A022856, A089071 and A133263. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 19 2008]
First differences are A001477.
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (3,-3,1).
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FORMULA
| a(n) = a(n-1)+n-2 (with a(1)=2). [From Vincenzo Librandi, Nov 26 2010]
a(n) = 3*a(n-1)-3*a(n-2)+a(n-3).
G.f. -x*(2-4*x+3*x^2) / (x-1)^3 . - R. J. Mathar, Oct 30 2011
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MATHEMATICA
| s=2; lst={2}; Do[s+=n; AppendTo[lst, s], {n, 0, 5!}]; lst
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PROG
| (SAGE) [2+binomial(n, 2) for n in xrange(0, 54)] # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 12 2009]
(MAGMA) [ (n^2-3*n+6)/2: n in [1..60] ];
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CROSSREFS
| Cf. A000217, A152947, A000124.
Sequence in context: A179523 A087729 A039890 * A018136 A022863 A039822
Adjacent sequences: A152945 A152946 A152947 * A152949 A152950 A152951
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KEYWORD
| nonn,easy
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AUTHOR
| Vladimir Orlovsky (4vladimir(AT)gmail.com), Dec 15 2008
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