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A120729
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Smallest integer k>0 such that k*10^n + 1 is a semiprime.
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0
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3, 2, 2, 5, 1, 1, 1, 1, 1, 2, 4, 2, 3, 7, 4
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| The corresponding semiprimes are 4, 21, 201, 5001, 10001, 100001, 100001, 10000001, 2000000001, 40000000001, ... Semiprime analogue of A121172.
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FORMULA
| Smallest integer k>0 such that k*10^n + 1 is in A001358.
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EXAMPLE
| a(0) = 3 because 3*10^0 + 1 = 4 = 2^2 is a semiprime.
a(1) = 2 because 2*10^1 + 1 = 21 = 3*7 is a semiprime.
a(2) = 2 because 2*10^2 + 1 = 201 = 3*67 is a semiprime.
a(3) = 5 because 5*10^3 + 1 = 5001 = 3*1667 is a semiprime.
a(4) = 1 because 1*10^4 + 1 = 10001 = 73*137 is a semiprime.
a(5) = 1 because 1*10^5 + 1 = 100001 = 11*9091 is a semiprime.
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CROSSREFS
| Cf. A001358, A030430, A037071, A062800, A065582, A121172.
Sequence in context: A111241 A192183 A133518 * A205139 A092743 A139420
Adjacent sequences: A120726 A120727 A120728 * A120730 A120731 A120732
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KEYWORD
| easy,nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Aug 17 2006
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