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A081271
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Vertical of triangular spiral in A051682.
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4
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1, 13, 34, 64, 103, 151, 208, 274, 349, 433, 526, 628, 739, 859, 988, 1126, 1273, 1429, 1594, 1768, 1951, 2143, 2344, 2554, 2773, 3001, 3238, 3484, 3739, 4003, 4276, 4558, 4849, 5149, 5458, 5776, 6103, 6439, 6784, 7138, 7501, 7873, 8254, 8644, 9043, 9451
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Lies to the right of the y-axis of the triangle.
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FORMULA
| a(n)=C(n, 0)+12C(n, 1)+9C(n, 2); binomial transform of (1, 12, 9, 0, 0, 0, .....). a(n)=(9n^2+15n+2)/2. G.f.(1+10x-2x^2)/(1-x)^3.
a(0) = 1, a(n) = a(n-1) + 9*n + 3 for n > 0 - Gerald McGarvey (Gerald.McGarvey(AT)comcast.net), Aug 18 2004
a(n)=9*n+a(n-1)+3 (with a(0)=1) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Aug 08 2010]
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EXAMPLE
| a(1)=9*1+1+3=13; a(2)=9*2+13+3=34; a(3)=9*3+34+3=64 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Aug 08 2010]
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CROSSREFS
| Cf. A062741.
Sequence in context: A164539 A134864 A093100 * A190458 A180673 A081752
Adjacent sequences: A081268 A081269 A081270 * A081272 A081273 A081274
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Mar 15 2003
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