%N Nonsquare numbers k such that k and k + 1 are semiprimes.
%C If n and n+1 are semiprimes then n+1 is always nonsquare while n can be a full square (see A263951). The sequence gives the nonsquare terms of A070552. Each of the numbers n and n+1 is a product of two distinct primes.
%C Numbers that are terms in A070552 but not in A263951.
%C The subsequence of triples of consecutive squarefree semiprimes is A039833. - _R. J. Mathar_, Aug 13 2019
%H Seiichi Manyama, <a href="/A263990/b263990.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range, ! IntegerQ[Sqrt[#]] && 2 == PrimeOmega[#] == PrimeOmega[# + 1] &]
%o (PARI) is(n)=if(n%2, isprime((n+1)/2) && bigomega(n)==2 && !isprimepower(n), isprime(n/2) && bigomega(n+1)==2) \\ _Charles R Greathouse IV_, Apr 25 2016
%Y Subsequence of A070552, A086263.
%Y Cf. A006881, A263951.
%A _Zak Seidov_, Oct 31 2015