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A172294
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Sequence of the "Natural Jewels": a natural jewel is a number that is totally enclosed by prime numbers in a version of Ulam Spiral.
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2
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12, 42, 1152, 1452, 1950, 3672, 5520, 6660, 8232, 10890, 13218, 15288, 15360, 16062, 18042, 20898, 21018, 23562, 23628, 25998, 27918, 32190, 37812, 42018, 42462, 48858, 55818, 57192, 80832, 80910, 83232, 83340, 91368, 97848, 98640
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OFFSET
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1,1
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COMMENTS
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There is no formula to calculate these numbers. If the sequence is infinite, then there are infinitely many primes p such that p + 2 is also prime (twin prime conjecture).
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LINKS
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EXAMPLE
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11-(top)->12, 13-(left)->12, 29-(right)->12, 31-(bottom)->12.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Emilio Apricena (emilioapricena(AT)yahoo.it), Jan 30 2010
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EXTENSIONS
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Corrected and extended by Emilio Apricena (emilioapricena(AT)yahoo.it), May 15 2010
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STATUS
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approved
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