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A133517
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Smallest k such that p(n)^3 - k is prime where p(n) is the n-th prime.
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7
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1, 4, 12, 6, 4, 18, 4, 2, 4, 10, 2, 2, 4, 14, 10, 4, 22, 38, 2, 28, 14, 12, 4, 22, 24, 4, 14, 24, 2, 10, 14, 4, 16, 12, 10, 2, 12, 30, 10, 16, 48, 18, 10, 20, 30, 42, 2, 14, 4, 26, 18, 10, 2, 10, 4, 4, 16, 12, 2, 34, 24, 58, 30, 4, 38, 6, 14, 14, 10, 12, 36, 6, 2, 24, 68, 4, 6, 26, 10
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| p(4)=7, 7^3 = 343; for odd k and n > 1, p(n)^r - k is even and thus not prime, so we only need consider even k.
for k = 2: 343 - 2 = 341, which is 11 * 31 and not prime.
for k = 4: 343 - 4 = 339, which is 3 * 113, also not prime.
for k = 6: 343 - 6 = 337, which is prime, so 6 is the smallest number that can be subtracted from 343 to make another prime.
Hence a(4) = 6.
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CROSSREFS
| Cf. A030078, A054271, A091666, A133518, A133519, A133520, A133521, A133522, (A001223).
Sequence in context: A084351 A203031 A190392 * A145046 A205849 A084415
Adjacent sequences: A133514 A133515 A133516 * A133518 A133519 A133520
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KEYWORD
| easy,nonn
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AUTHOR
| Carl R. White (oeisfan(AT)phodd.net), Sep 14 2007
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