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 A212785 #8 Jul 22 2025 22:57:40 %S A212785 13,162,1238,5104,16594,43727,101743,211461,408430,735896,1261599, %T A212785 2064329,3259612,4975687,7395946,10715635,15205983,21151890,28937100, %U A212785 38956477,51737361,67810309,87873466,112625630,142969752,179799242 %N A212785 Half the number of 0..n arrays of length 6 with second differences nonzero. %C A212785 Row 4 of A212782 %H A212785 R. H. Hardin, <a href="/A212785/b212785.txt">Table of n, a(n) for n = 1..210</a> %F A212785 Empirical: a(n) = a(n-2) +2*a(n-3) +2*a(n-4) -a(n-5) -2*a(n-6) -5*a(n-7) -3*a(n-8) +3*a(n-10) +6*a(n-11) +5*a(n-12) +3*a(n-13) -3*a(n-14) -5*a(n-15) -6*a(n-16) -3*a(n-17) +3*a(n-19) +5*a(n-20) +2*a(n-21) +a(n-22) -2*a(n-23) -2*a(n-24) -a(n-25) +a(n-27) %e A212785 Some solutions for n=5 %e A212785 ..2....2....5....1....3....3....5....4....0....5....3....3....3....4....2....2 %e A212785 ..0....4....1....4....5....0....2....0....1....4....5....4....4....3....5....1 %e A212785 ..5....3....3....5....3....3....0....0....1....1....1....0....4....5....4....3 %e A212785 ..4....3....2....3....4....5....0....5....0....5....3....4....1....0....0....2 %e A212785 ..0....1....4....5....4....2....1....4....5....2....2....3....0....5....3....2 %e A212785 ..5....2....1....4....5....3....0....5....3....5....4....1....0....5....5....5 %K A212785 nonn %O A212785 1,1 %A A212785 _R. H. Hardin_ May 27 2012