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 A157484 #13 Jul 10 2025 14:08:12
%S A157484 55,89,151,197,233,249,295,307,329,341,343,349,461,489,491,569,571,
%T A157484 665,713,739,775,851,857,859,869,871,949,1013,1015,1061,1097,1111,
%U A157484 1149,1191,1205,1207,1209,1211,1219,1255,1275,1277,1291,1303,1315,1421,1431,1449,1483
%N A157484 Numbers k such that k+-1 are divisible by exactly 4 primes, counted with multiplicity.
%H A157484 Harvey P. Dale, <a href="/A157484/b157484.txt">Table of n, a(n) for n = 1..2000</a>
%e A157484 55 is a term: 55-1 = 54 = 2*3*3*3 and 55+1 = 56 = 2*2*2*7.
%t A157484 q=4;lst={};Do[If[Plus@@Last/@FactorInteger[n-1]==q&&Plus@@Last/@FactorInteger[n+1]==q,AppendTo[lst,n]],{n,7!}];lst
%t A157484 SequencePosition[PrimeOmega[Range[1200]],{4,_,4}][[All,1]]+1 (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, May 08 2019 *)
%o A157484 (PARI) is(k) = bigomega(k-1)==4 && bigomega(k+1)==4; \\ _Jinyuan Wang_, Mar 22 2020
%Y A157484 Cf. A014612, A124936, A157483.
%K A157484 nonn
%O A157484 1,1
%A A157484 _Vladimir Joseph Stephan Orlovsky_, Mar 01 2009