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 A101031 #3 Mar 30 2012 18:57:06 %S A101031 0,0,1,0,1,7,0,1,15,58,0,1,31,196,601,0,1,63,634,2765,7656,0,1,127, %T A101031 1996,12265,44136,116929,0,1,255,6178,52925,248016,803383,2092112,0,1, %U A101031 511,18916,223801,1362096,5432161,16595776,43006401,0,1,1023,57514,932525 %N A101031 Triangle read by rows: T(n,k) = (1/k) times the number of functions from an n-element set into but not onto a k-element set. %F A101031 T(n, k) = (A089072(n, k)-A019538(n, k))/k (where the two sequences are indexed as triangular arrays). %e A101031 T(3,3) = (1/3)*[ #(functions into) - #(functions onto)] = (3^3 - 6)/3 = 7. %K A101031 nonn,tabl %O A101031 0,6 %A A101031 _Clark Kimberling_, Nov 26 2004