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 A280469 #8 Jan 30 2017 14:00:38
%S A280469 4,6,12,18,30,34,42,56,60,72,86,92,94,102,108,138,142,144,150,160,180,
%T A280469 184,186,192,198,202,204,214,216,218,220,228,236,240,248,266,270,282,
%U A280469 300,302,304,312,320,322,328,340,348,392,394,412,414,416,420,432,446
%N A280469 Numbers n such that n-1 and n+1 are squarefree and have the same number of prime factors.
%C A280469 For a given term n of this sequence, n-1 and n+1 are both squarefree k-almost primes for the same k. The sequence is thus the union of the averages (arithmetic means) of twin prime pairs (A014574), the averages of twin squarefree semiprime pairs, the averages of twin squarefree 3-almost prime pairs, ... (where "twin ... pairs" means the members of each pair differ by two). A subsequence of A280382 and of A280383.
%H A280469 Rick L. Shepherd, <a href="/A280469/b280469.txt">Table of n, a(n) for n = 1..10000</a>
%e A280469 The number 34 is a term because 33 = 3*11 and 35 = 5*7, a twin semiprime pair. Unlike A280382 and A280383, 19 is not a term here because 18 = 2*3^2 and 20 = 2^2*5, neither of which is squarefree.
%t A280469 Select[Range@ 500, And[Times @@ First@ # == 1, SameQ @@ Last@ #] &@ Transpose@ Map[{Boole@ SquareFreeQ@ #, PrimeNu@ #} &, # + {-1, 1}] &] (* _Michael De Vlieger_, Jan 30 2017 *)
%o A280469 (PARI) IsInA280469(n) = n > 1 && issquarefree(n-1) && issquarefree(n+1) && omega(n-1) == omega(n+1)
%Y A280469 Cf. A014574, A280382, A280383.
%K A280469 nonn
%O A280469 1,1
%A A280469 _Rick L. Shepherd_, Jan 03 2017