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Search: id:A117406
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| 3, 2, 0, 1, -2, 1, 1, 1, 1, -2, -1, 3, -1, 1, 1, -2, -3, -5, 1, -2, 1, 1
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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After n=2, never again is a(n) = 0. Semiprime analogue of A117388 Integer k such that 2^n + k = A117387(n). A117387(n) is prime nearest to 2^n. (In case of a tie, choose the smaller).
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FORMULA
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a(n) = A117405(n) - 2^n. a(n) = Min{k such that A001358(i) + k = 2^j}.
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EXAMPLE
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a(0) = 3 because 2^0 + 3 = 4 = A001358(1), and no semiprime is closer to 2^0.
a(1) = 2 because 2^1 + 2 = 4 = A001358(1), and no semiprime is closer to 2^1.
a(2) = 0 because 2^2 + 0 = 4 = A001358(1), and no semiprime is closer to 2^2.
a(3) = 1 because 2^3 + 1 = 9 = 3^2 = A001358(3), no semiprime is closer to 2^3.
a(4) = -2 because 2^4 - 2 = 14 = 2 * 7 = A001358(5), no semiprime is closer.
a(5) = 1 because 2^5 + 1 = 33 = 3 * 11, and no semiprime is closer to 2^5.
a(6) = 1 because 2^6 + 1 = 65 = 5 * 13, and no semiprime is closer to 2^6.
a(7) = 1 because 2^7 + 1 = 129 = 3 * 43, and no semiprime is closer to 2^7.
a(8) = -2 because 2^8 - 2 = 254 = 2 * 127, and no semiprime is closer to 2^8.
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CROSSREFS
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Cf. A000079, A001358, A117387, A117405.
Adjacent sequences: A117403 A117404 A117405 this_sequence A117407 A117408 A117409
Sequence in context: A116604 A138741 A079618 this_sequence A008783 A081576 A054654
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KEYWORD
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easy,sign,less
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Mar 13 2006
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