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 A161811 #5 Jul 08 2022 19:08:43 %S A161811 4,5,4,3,2,3,4,3,2,3,4,3,2,3,3,2,2,2,3,4,3,2,2,2,3,3,2,3,4,3,2,3,3,2, %T A161811 2,2,3,3,2,2,2,3,4,3,2,2,2,3,3,2,3,4,3,2,2,2,3,3,2,3,3,2,2,2,3,3,2,2, %U A161811 2,2,2,3,3,2,3,4,3,2,3,4,3,2,3,3,2,2,2,2,2,2,2,2,2,2,2,3,3,2,3,3,2,2,2,3,4 %N A161811 Difference between nonprime(n+2) and nonprime(n). %C A161811 "nonprime(n)" is used for "n-th nonprime". Here the nonprimes start at 0 (see A141468), so nonprime(1) to nonprime(15) are 0, 1, 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22. %F A161811 a(n) = A141468(n+2)-A141468(n). %e A161811 nonprime(1+2)-nonprime(1) = 4-0; so a(1) = 4. %e A161811 nonprime(5+2)-nonprime(5) = 10-8; so a(5) = 2. %e A161811 nonprime(11+2)-nonprime(11) = 20-16; so a(11) = 4. %t A161811 #[[3]]-#[[1]]&/@Partition[Select[Range[0,150],!PrimeQ[#]&],3,1] (* _Harvey P. Dale_, Jul 08 2022 *) %Y A161811 Cf. A031131, A141468. %K A161811 nonn %O A161811 1,1 %A A161811 _Juri-Stepan Gerasimov_, Jun 20 2009 %E A161811 Edited, corrected (a(11)=2 replaced by 4) and extended by _Klaus Brockhaus_, Jun 24 2009