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%I #17 Jul 07 2016 06:31:56
%S 1,23,163,281,431,613,827,2003,2377,3221,3691,6521,7877,10151,10973,
%T 11827,12713,17623,18701,23333,24571,25841,27143,28477,38711,43577,
%U 45263,48731,50513,65921,72227,81083,85703,95327,97813,102881,124433
%N Noncomposite numbers in the southern ray of the Ulam spiral as oriented on the March 1964 cover of Scientific American.
%H G. C. Greubel, <a href="/A168027/b168027.txt">Table of n, a(n) for n = 0..1000</a>
%H Alonso del Arte, <a href="http://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 + 3n + 1 with no more than two divisors.
%t Select[Table[4 n^2 + 3 n + 1, {n, 0, 199}], Length[Divisors[ # ]] < 3 &]
%Y Cf. A033951, all numbers of the form 4n^2 + 3n + 1. Noncomposites of the eastern ray are in A168022. Primes of the northeastern ray are in A073337. Noncomposites of the northern ray are in A168023. Primes of the northwestern ray are in A121326. Noncomposites of the western ray are in A168025. Noncomposites of the southwestern ray are in A168026. There are no primes on the southeastern ray, which, being A016754, are the odd squares, and thus none of them are prime.
%K easy,nonn
%O 0,2
%A _Alonso del Arte_, Nov 16 2009
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