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A081438
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Diagonal in array of n-gonal numbers A081422.
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4
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1, 11, 36, 82, 155, 261, 406, 596, 837, 1135, 1496, 1926, 2431, 3017, 3690, 4456, 5321, 6291, 7372, 8570, 9891, 11341, 12926, 14652, 16525, 18551, 20736, 23086, 25607, 28305, 31186, 34256, 37521, 40987, 44660, 48546, 52651, 56981, 61542, 66340
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| One of a family of sequences with palindromic generators.
a(n) = (A177058(n+3)+A177058(n+2))/2. E.g., a(5) = (A177058(8)+A177058(7))/2 = (323+199)/2 = 261. [From Bruno Berselli (berselli.bruno(AT)yahoo.it), Jun 04 2010]
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FORMULA
| a(n)=(2n^3+9n^2+9n+2)/2. G.f. (1+6x-9x^2+2x^3)/(1-x)^5.
Contribution from Bruno Berselli (berselli.bruno(AT)yahoo.it), Jun 04 2010: (Start)
G.f.: (1+7*x-2*x^2)/(1-x)^4 (simplified).
a(n) = (n+1)*(2*n^2+7*n+2)/2.
a(n)-4*a(n-1)+6*a(n-2)-4*a(n-3)+a(n-4) = 0, with n>3. (End)
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CROSSREFS
| Cf. A081436, A081437, A081441.
Cf. A177058. [From Bruno Berselli (berselli.bruno(AT)yahoo.it), Jun 04 2010]
Sequence in context: A044469 A015246 A093500 * A160483 A034309 A005000
Adjacent sequences: A081435 A081436 A081437 * A081439 A081440 A081441
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Mar 21 2003
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