%I #12 Jan 23 2020 14:38:55
%S 2,5,10,17,26,37,65,82,101,122,145,197,226,257,362,401,485,577,626,
%T 677,785,842,901,1157,1226,1297,1522,1601,1765,1937,2026,2117,2305,
%U 2402,2501,2602,2705,2917,3137,3365,3482,3601,3722,3845,4097,4226,4357,4762
%N Numbers of the form x^2+1 with at most two prime factors.
%C Prime factors are counted with multiplicity, as in A144255.
%C Iwaniec shows that the sequence is infinite.
%H Charles R Greathouse IV, <a href="/A248742/b248742.txt">Table of n, a(n) for n = 1..10000</a>
%H H. Iwaniec, <a href="http://dx.doi.org/10.1007/BF01578070">Almost-primes represented by quadratic polynomials</a>, Inventiones Mathematicae 47:2 (1978), pp. 171-188.
%H Vishaal Kapoor, <a href="https://arxiv.org/abs/1910.02885">Almost-primes represented by quadratic polynomials</a>, MS thesis (2006). arXiv:1910.02885 [math.NT]
%H Robert J. Lemke Oliver, <a href="https://math.tufts.edu/faculty/rlemkeoliver/papers/04-Quadratic.pdf">Almost-primes represented by quadratic polynomials</a>, Acta Arithm. 151 (2012) 241. DOI: <a href="http://dx.doi.org/10.4064/aa151-3-2">10.4064/aa151-3-2</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Landau%27s_problems">Landau's problems</a>
%F A002496 UNION A144255.
%o (PARI) is(n)=issquare(n-1) && bigomega(n)<3 \\ _Charles R Greathouse IV_, Feb 05 2017
%Y Cf. A002496, A069987.
%K nonn
%O 1,1
%A _R. J. Mathar_, Oct 13 2014