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A168027
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Non-composite numbers in the southern ray of the Ulam spiral as oriented on the March 1964 cover of Scientific American.
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4
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1, 23, 163, 281, 431, 613, 827, 2003, 2377, 3221, 3691, 6521, 7877, 10151, 10973, 11827, 12713, 17623, 18701, 23333, 24571, 25841, 27143, 28477, 38711, 43577, 45263, 48731, 50513, 65921, 72227, 81083, 85703, 95327, 97813, 102881, 124433
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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LINKS
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Table of n, a(n) for n=0..36.
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FORMULA
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Positive numbers of the form 4n^2 + 3n + 1 with no more than two divisors.
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MATHEMATICA
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Select[Table[4 n^2 + 3 n + 1, {n, 0, 199}], Length[Divisors[ # ]] < 3 &]
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CROSSREFS
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Cf. A033951, all numbers of the form 4n^2 + 3n + 1. Non-composites of eastern ray are in A168022. Primes of northeastern ray are in A073337. Non-composites of northern ray are in A168023. Primes of northwestern ray are in A121326. Non-composites of western ray are in A168025. Non-composites of 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 prime.
Sequence in context: A214895 A042022 A142091 * A155842 A186260 A125360
Adjacent sequences: A168024 A168025 A168026 * A168028 A168029 A168030
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KEYWORD
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easy,nonn
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AUTHOR
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Alonso del Arte, Nov 16 2009
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STATUS
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approved
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