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 A212781 #6 Jul 22 2025 22:57:21 %S A212781 240,1803,13544,101743,764297,5741427,43129809,323992699,2433844978, %T A212781 18283132290,137343556947,1031729811702,7750391995200,58221227493827, %U A212781 437359985531993,3285464171376777,24680526747938834,185401017567775934 %N A212781 Half the number of 0..7 arrays of length n+2 with second differences nonzero. %C A212781 Column 7 of A212782 %H A212781 R. H. Hardin, <a href="/A212781/b212781.txt">Table of n, a(n) for n = 1..210</a> %F A212781 Empirical: a(n) = 4*a(n-1) +22*a(n-2) +33*a(n-3) +5*a(n-4) -36*a(n-5) -40*a(n-6) -28*a(n-7) -53*a(n-8) -73*a(n-9) -37*a(n-10) +12*a(n-11) +32*a(n-12) +39*a(n-13) +28*a(n-14) +6*a(n-15) %e A212781 Some solutions for n=5 %e A212781 ..1....0....1....0....1....1....1....1....0....0....0....0....1....1....0....0 %e A212781 ..4....0....6....2....4....0....4....6....4....6....0....6....0....6....0....0 %e A212781 ..6....7....7....6....3....6....1....1....2....5....5....5....1....2....5....4 %e A212781 ..0....6....6....2....0....6....2....2....4....2....1....0....5....4....2....6 %e A212781 ..0....3....0....7....1....7....0....4....0....1....4....3....1....5....5....1 %e A212781 ..1....3....4....0....6....5....5....7....3....1....4....3....0....0....6....6 %e A212781 ..4....6....5....6....4....5....4....4....5....7....5....0....6....7....4....4 %K A212781 nonn %O A212781 1,1 %A A212781 _R. H. Hardin_ May 27 2012