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