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%I #9 Sep 29 2023 07:56:44
%S 17,177,1429,9705,58141,320481,1688101,8717049,44633821,227363409,
%T 1153594261,5835080169,29443836301,148292923329,745759583941,
%U 3745977788889,18798608421181,94267920012849,472439111692021
%N Number of second differences of arrays of length n + 2 of numbers in 0..4.
%H R. H. Hardin, <a href="/A228214/b228214.txt">Table of n, a(n) for n = 1..137</a>
%F Empirical: a(n) = 9*a(n-1) - 20*a(n-2) = A005060(n+2) for n>9.
%F Conjectures from _Colin Barker_, Sep 10 2018: (Start)
%F G.f.: x*(17 + 24*x + 176*x^2 + 384*x^3 - 624*x^4 - 8688*x^5 - 33408*x^6 - 66240*x^7 - 57600*x^8) / ((1 - 4*x)*(1 - 5*x)).
%F a(n) = 5^(2+n) - 4^(2+n) for n>7.
%F (End)
%e Some solutions for n=4:
%e ..8....5...-1...-2....4...-2....3....0...-2...-6....2....0....4...-5....0...-5
%e .-8....0....2....2...-5...-4...-4...-2....2....5....2...-2...-3....4....2....5
%e ..5....0....0...-2...-1....7....3....2....4....0...-6....3...-1...-1...-6...-6
%e .-1...-2...-2....4....2...-3...-3....3...-7...-1....4...-3....6...-1....5....4
%Y Column 4 of A228218.
%K nonn
%O 1,1
%A _R. H. Hardin_, Aug 16 2013
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