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A033954
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Second 10-gonal (or decagonal) numbers: n*(4*n+3).
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33
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0, 7, 22, 45, 76, 115, 162, 217, 280, 351, 430, 517, 612, 715, 826, 945, 1072, 1207, 1350, 1501, 1660, 1827, 2002, 2185, 2376, 2575, 2782, 2997, 3220, 3451, 3690, 3937, 4192, 4455, 4726, 5005, 5292, 5587, 5890, 6201, 6520, 6847, 7182, 7525, 7876, 8235
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OFFSET
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0,2
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COMMENTS
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Bisection of A074377. Also sequence found by reading the line from 0, in the direction 0, 22... and the line from 7, in the direction 7, 45,..., in the square spiral whose vertices are the generalized 10-gonal numbers A074377. - Omar E. Pol, Jul 24 2012
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REFERENCES
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S. M. Ellerstein, The square spiral, J. Recreational Mathematics 29 (#3, 1998) 188; 30 (#4, 1999-2000), 246-250.
R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. Addison-Wesley, Reading, MA, 2nd ed., 1994, p. 99.
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LINKS
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Ivan Panchenko, Table of n, a(n) for n = 0..1000
Emilio Apricena, A version of the Ulam spiral
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
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FORMULA
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G.f.: x(7+x)/(1-x)^3. - Michael Somos, Mar 03 2003
a(n) = 8*n+a(n-1)-1 with a(0)=0. - Vincenzo Librandi, Jul 20 2010
For n>0, Sum{i=0..n} (a(n)+i)^4 + (4*A000217(n))^3 = Sum{i=n+1..2n} (a(n)+i)^4; see also A045944. - Charlie Marion, Dec 08 2007, edited by Michel Marcus, Mar 14 2014
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) with a(0) = 0, a(1) = 7, a(2) = 22. - Philippe Deléham, Mar 26 2013
a(n) = A118729(8n+6). - Philippe Deléham, Mar 26 2013
a(n) = A002943(n) + n = A007742(n) + 2n = A016742(n) + 3n = A033991(n) + 4n = A002939(n) + 5n = A001107(n) + 6n = A033996(n) - n. - Philippe Deléham, Mar 26 2013
Sum_{n>=1} 1/a(n) = 4/9 + Pi/6 - log(2) = 0.2748960394827980081... . - Vaclav Kotesovec, Apr 27 2016
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EXAMPLE
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16 17 18 19 ...
15 4 5 6 ...
14 3 0 7 ...
13 2 1 8 ...
For n=1, a(1)=8*1+0-1=7; n=2, a(2)=8*2+7-1=22; n=3, a(3)=8*3+22-1=45. - Vincenzo Librandi, Jul 20 2010
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MATHEMATICA
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s=0; lst={s}; Do[s+=n++ +7; AppendTo[lst, s], {n, 0, 7!, 8}]; lst (* Vladimir Joseph Stephan Orlovsky, Nov 16 2008 *)
Table[n(4n+3), {n, 0, 50}] (* or *) LinearRecurrence[{3, -3, 1}, {0, 7, 22}, 50] (* Harvey P. Dale, May 06 2018 *)
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PROG
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(PARI) a(n)=4*n^2+3*n
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CROSSREFS
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Same as A033951 except start at 0.
a(n)=A001107(-n)=A074377(2n).
Sequences from spirals: A001107, A002939, A007742, A033951, A033952, A033953, A033954, A033989, A033990, A033991, A002943, A033996, A033988.
Cf. A002620.
Second n-gonal numbers: A005449, A014105, A147875, A045944, A179986, this sequence, A062728, A135705.
Sequence in context: A275642 A171441 A261465 * A159227 A081274 A038764
Adjacent sequences: A033951 A033952 A033953 * A033955 A033956 A033957
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane
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STATUS
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approved
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