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 A357074 #9 Sep 11 2022 19:13:28 %S A357074 11,13,19,21,23,25,27,34,35,37,39,45,47,49,51,53,55,56,57,64,73,75,76, %T A357074 81,86,87,92,93,94,95,97,99,105,107,116,117,118,123,134,135,142,143, %U A357074 144,145,146,147,154,159,160,161,163,165,176,177,184,186,188,193,195 %N A357074 Numbers sandwiched between a pair of numbers each with exactly two prime factors (counted without multiplicity). %C A357074 Number k such that both k-1 and k+1 are in A007774. %e A357074 11 is sandwiched between 10 = 2*5 and 12 = 2^2*3. Both 10 and 12 have exactly two prime factors. Thus, 11 is in this sequence. %t A357074 Select[Range[1000],Length[FactorInteger[# + 1]] == 2 && Length[FactorInteger[# - 1]] == 2 &] %o A357074 (Python) %o A357074 from sympy import factorint %o A357074 def isA007774(n): return len(factorint(n)) == 2 %o A357074 def ok(n): return isA007774(n-1) and isA007774(n+1) %o A357074 print([k for k in range(200) if ok(k)]) # _Michael S. Branicky_, Sep 10 2022 %Y A357074 Cf. A007774. %K A357074 nonn %O A357074 1,1 %A A357074 _Tanya Khovanova_, Sep 10 2022