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Search: id:A117417
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| 3, 1, 0, -1, 1, 4, 2, -1, -2, -4, -2, 2, -2, -1, 10, -2, 1, -4, 4, -2, -2, -2, -12, -4, 8, -2
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OFFSET
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0,1
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COMMENT
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Distance from 3^n to the nearest semiprime. See also: A117405 Semiprime nearest to 2^n. A117387 Prime nearest to 2^n.
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FORMULA
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a(n) = Integer k such that 3^n + k = A117416(n). a(n) = A117416(n) - 3^n. a(n) = Min{k such that A001358(i) + k = 3^n}.
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EXAMPLE
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a(0) = 3 because 3^0 + 3 = 4 = A001358(1), and no semiprime is closer to 3^0.
a(1) = 1 because 3^1 + 1 = 4 = A001358(1), and no semiprime is closer to 3^1.
a(2) = 0 because 3^2 + 0 = 9 = 3^2 = A001358(3), no semiprime is closer to 3^2 [this is the only 0 element].
a(3) = -1 because 3^3 - 1 = 26 = 2 * 13, no semiprime is closer.
a(4) = 1 because 3^4 + 1 = 82 = 2 * 41, no semiprime is closer.
a(5) = 4 because 3^5 + 4 = 247 = 13 * 19, no semiprime is closer.
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CROSSREFS
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Cf. A000079, A001358, A117387, A117405, A117406, A117416.
Sequence in context: A060096 A051834 A062719 this_sequence A053382 A031253 A122779
Adjacent sequences: A117414 A117415 A117416 this_sequence A117418 A117419 A117420
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KEYWORD
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easy,sign,less
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 13 2006
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