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A244806
The 180-degree spoke (or ray) of a hexagonal spiral of Ulam.
7
1, 18, 59, 124, 213, 326, 463, 624, 809, 1018, 1251, 1508, 1789, 2094, 2423, 2776, 3153, 3554, 3979, 4428, 4901, 5398, 5919, 6464, 7033, 7626, 8243, 8884, 9549, 10238, 10951, 11688, 12449, 13234, 14043, 14876, 15733, 16614, 17519, 18448, 19401, 20378, 21379, 22404, 23453, 24526, 25623
OFFSET
1,2
FORMULA
a(n) = 12*n^2 - 19*n + 8.
See A056105 example section for its formula.
From Colin Barker, Dec 12 2016: (Start)
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>3.
G.f.: x*(1 + 15*x + 8*x^2) / (1 - x)^3.
(End)
EXAMPLE
See A056105 example section for its diagram.
MAPLE
A244806:=n->12*n^2 - 19*n + 8: seq(A244806(n), n=1..50); # Wesley Ivan Hurt, Jul 06 2014
MATHEMATICA
f[n_] := 12n^2 - 19n + 8; Array[f, 47]
PROG
(PARI) vector(50, n, 12*n^2 - 19*n + 8) \\ Michel Marcus, Jul 06 2014
(PARI) Vec(x*(1 + 15*x + 8*x^2) / (1 - x)^3 + O(x^50)) \\ Colin Barker, Dec 12 2016
(Magma) [12*n^2 - 19*n + 8 : n in [1..50]]; // Wesley Ivan Hurt, Jul 06 2014
KEYWORD
nonn,easy
AUTHOR
Robert G. Wilson v, Jul 06 2014
STATUS
approved