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%I #18 Jan 23 2018 07:55:27
%S 1,19,151,1621,2731,3631,4129,7789,11719,12601,14461,15439,17491,
%T 20809,28309,29671,32491,41719,59659,69829,78541,83089,85411,92569,
%U 97501,115771,132679,138571
%N Noncomposite numbers in the western ray of the Ulam spiral as oriented on the March 1964 cover of Scientific American.
%H G. C. Greubel, <a href="/A168025/b168025.txt">Table of n, a(n) for n = 0..1000</a>
%H Alonso del Arte, <a href="https://www.youtube.com/watch?v=dx24qqBc-PY">Ulam spiral</a> (2009). [Note that "East" and "West" in this video match the cover of Scientific American, but "North" and "South" are switched.]
%H BackIssues.com, <a href="http://backissues.com/issue/Scientific-American-March-1964">Scientific American March 1964 back issue</a>
%H MathWorld, <a href="http://mathworld.wolfram.com/PrimeSpiral.html">Prime Spiral</a>
%H Scientific American, <a href="/A168022/a168022.pdf">March 1964 cover</a>
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Ulam_spiral#Construction">Ulam Spiral</a>
%F Positive numbers of the form 4n^2 - 7n + 4 with no more than two divisors.
%t Select[Table[4 n^2 - 7 n + 4, {n, 0, 199}], Length[Divisors[ # ]] < 3 &]
%Y Cf. A054567.
%K easy,nonn
%O 0,2
%A _Alonso del Arte_, Nov 16 2009
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