This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A212780 #6 Jul 22 2025 22:57:14 %S A212780 159,1034,6724,43727,284360,1849215,12025596,78203437,508563345, %T A212780 3307229006,21507180645,139862954332,909540228150,5914814473647, %U A212780 38464522156756,250137932701244,1626667429300337,10578351299907331 %N A212780 Half the number of 0..6 arrays of length n+2 with second differences nonzero. %C A212780 Column 6 of A212782 %H A212780 R. H. Hardin, <a href="/A212780/b212780.txt">Table of n, a(n) for n = 1..210</a> %F A212780 Empirical: a(n) = 3*a(n-1) +15*a(n-2) +39*a(n-3) +66*a(n-4) +65*a(n-5) -3*a(n-6) -107*a(n-7) -162*a(n-8) -136*a(n-9) -96*a(n-10) -71*a(n-11) -31*a(n-12) -4*a(n-13) %e A212780 Some solutions for n=5 %e A212780 ..0....0....3....0....0....0....0....0....0....4....0....4....0....0....0....0 %e A212780 ..4....2....0....0....0....3....5....4....0....0....6....0....5....5....1....6 %e A212780 ..6....2....4....2....2....0....0....1....3....1....6....0....0....1....3....4 %e A212780 ..3....5....6....0....3....1....4....4....0....0....2....5....2....1....6....4 %e A212780 ..2....1....1....3....2....3....4....6....6....5....1....1....5....0....4....1 %e A212780 ..6....2....6....1....6....3....3....1....0....6....4....2....2....1....3....1 %e A212780 ..2....0....3....1....4....1....6....5....6....1....3....1....2....4....0....0 %K A212780 nonn %O A212780 1,1 %A A212780 _R. H. Hardin_ May 27 2012