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A102415
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Greatest semiprime less than n-th prime.
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5
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4, 6, 10, 10, 15, 15, 22, 26, 26, 35, 39, 39, 46, 51, 58, 58, 65, 69, 69, 77, 82, 87, 95, 95, 95, 106, 106, 111, 123, 129, 134, 134, 146, 146, 155, 161, 166, 169, 178, 178, 187, 187, 194, 194, 209, 221, 226, 226, 226, 237, 237, 249, 254, 262, 267, 267, 274, 278, 278
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OFFSET
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3,1
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LINKS
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Amiram Eldar, Table of n, a(n) for n = 3..10000
Eric Weisstein's World of Mathematics, Semiprime
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FORMULA
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a(n) < A000040(n) < A102414(n).
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EXAMPLE
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a(3) = 4 since 4 is the greatest semiprime less than prime(3) = 5.
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MATHEMATICA
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a[n_] := Module[{m = Prime[n] - 1}, While[PrimeOmega[m] != 2, m--]; m]; Array[a, 60, 3] (* Amiram Eldar, Feb 06 2020 *)
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PROG
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(PARI) a(n) = {sp = prime(n)-1; while(bigomega(sp) != 2, sp--); sp; } \\ Michel Marcus, Mar 04 2017
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CROSSREFS
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Cf. A001358, A102414, A102440.
Sequence in context: A193951 A129854 A088682 * A117003 A335032 A057670
Adjacent sequences: A102412 A102413 A102414 * A102416 A102417 A102418
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller, Jan 08 2005
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STATUS
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approved
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