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 A007975 #22 Apr 01 2025 03:27:33 %S A007975 2,55,389,1563,4642,11407,24600,48204,87758,150707,246787,388445, %T A007975 591294,874603,1261822,1781142,2466090,3356159,4497473,5943487, %U A007975 7755722,10004535,12769924,16142368,20223702,25128027,30982655,37929089,46124038,55740467,66968682,80017450,95115154,112510983,132476157,155305187,181317170 %N A007975 Number of permutations that are 3 "block reversals" away from 12...n. %F A007975 a(n) = A228397(n) - A228396(n). See C. Homberger links from A228396. - _Martin Fuller_, Mar 31 2025 %Y A007975 Cf. A007972, A007973, A007974. %Y A007975 Cf. A000124, A228396, A228397. %Y A007975 Column k=3 of A300003. %K A007975 nonn %O A007975 4,1 %A A007975 _J. H. Conway_ %E A007975 More terms from _Sean A. Irvine_, Feb 22 2018 %E A007975 a(34) onwards from _Martin Fuller_, Mar 31 2025