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 A075026 #10 Sep 28 2021 17:28:32 %S A075026 9,25,49,51,55,65,69,77,91,111,115,121,125,129,153,155,161,169,175, %T A075026 183,185,187,209,221,235,237,247,249,259,265,267,274,287,289,291,295, %U A075026 305,309,319,321,323,329,339,341,343,351,355,361,365,369,371,377,386,391 %N A075026 Define a number k to occupy a divisor cavity if d(k-1) > d(k) < d(k+1) where d(k) is the number of divisors of k. Sequence gives composite numbers occupying a divisor cavity. %p A075026 q:= k-> not isprime(k) and (d-> %p A075026 d(k-1)>d(k) and d(k)<d(k+1))(numtheory[tau]): %p A075026 select(q, [$1..400])[]; # _Alois P. Heinz_, Sep 28 2021 %t A075026 Select[Flatten[Position[Partition[DivisorSigma[0,Range[400]],3,1],_?(#[[1]]> #[[2]]<#[[3]]&),1,Heads->False]]+1,CompositeQ] (* _Harvey P. Dale_, Oct 23 2019 *) %Y A075026 Cf. A000005, A075025, A075027. %K A075026 nonn %O A075026 0,1 %A A075026 _Amarnath Murthy_, Sep 02 2002 %E A075026 Corrected and extended by _Jason Earls_, Sep 04 2002