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9, 49, 121, 225, 361, 529, 729, 961, 1225, 1521, 1849, 2209, 2601, 3025, 3481, 3969, 4489, 5041, 5625, 6241, 6889, 7569, 8281, 9025, 9801, 10609, 11449, 12321, 13225, 14161, 15129, 16129, 17161, 18225
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| If Y is a fixed 2-subset of a (4n+1)-set X then a(n-1) is the number of 3-subsets of X intersecting Y. - Milan R. Janjic (agnus(AT)blic.net), Oct 21 2007
A bisection of A016754. Sequence arises from reading the line from 9, in the direction 9, 49,... in the square spiral whose vertices are the squares A000290. - Omar E. Pol (info(AT)polprimos.com), May 24 2008
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 0..860
Milan Janjic, Two Enumerative Functions
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FORMULA
| Denominators of first differences Zeta[2,(4n-1)/4]-Zeta[2,(4(n+1)-1)/4] [From Artur Jasinski (grafix(AT)csl.pl), Mar 03 2010]
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MATHEMATICA
| Table[Denominator[RootApproximant[N[Zeta[2, (4 n - 1)/4] - Zeta[2, (4 (n + 1) - 1)/4], 100], 1]], {n, 1, 20}] [From Artur Jasinski (grafix(AT)csl.pl), Mar 03 2010]
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PROG
| (MAGMA) [(4*n+3)^2: n in [0..50]]; // Vincenzo Librandi, Apr 26 2011
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CROSSREFS
| Cf. A000290, A001539, A016742, A016754, A016802, A016814, A016826.
Sequence in context: A039940 A012111 A138998 * A087691 A014730 A164343
Adjacent sequences: A016835 A016836 A016837 * A016839 A016840 A016841
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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