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COMMENTS
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Write 1,2,3,4,... in a hexagonal spiral around 0, then a(n) is the sequence found by reading the line from 0 in the direction 0,4,... - Floor van Lamoen (fvlamoen(AT)hotmail.com), Jul 21 2001. The spiral begins:
......16..15..14
....17..5...4...13
..18..6...0...3...12
19..7...1...2...11..26
..20..8...9...10..25
....21..22..23..24
Number of edges in the join of the complete bipartite graph of order 2n and the cycle graph of order n, K_n,n * C_n - Roberto E. Martinez II (remartin(AT)fas.harvard.edu), Jan 07 2002
The average of the first n elements starting from a(1) is equal to (n+1)^2. - Mario Catalani (mario.catalani(AT)unito.it), Apr 10 2003
If Y is a 4-subset of an n-set X then, for n>=4, a(n-4) is the number of (n-4)-subsets of X having either one element or two elements in common with Y. - Milan Janjic, Dec 28 2007
The maximum possible sum of numbers in an N x N standard Minesweeper grid. [From Dmitry Kamenetsky, Dec 14 2008]
a(n) = A001399(6n-2), number of partitions of 6*n-2 into parts <4. For example a(2)=14 where the partitions of 6*2-2=10 into parts <4 are [1,1,1,1,1,1,1,1,1,1] [1,1,1,1,1,1,1,1,2] [1,1,1,1,1,1,1,3], [1,1,1,1,1,1,2,2] [1,1,1,1,1,2,3][1,1,1,1,2,2,2] [1,1,1,1,3,3], [1,1,1,2,2,3], [1,1,2,2,2,2] [1,1,2,3,3] [1,2,2,2,3], [2,2,2,2,2] [1,3,3,3], [2,2,3,3]. - Adi Dani, Jun 07 2011
a(n) = A100104(n+1) - A100104(n). - Reinhard Zumkeller, Jul 07 2012
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