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Search: id:A109024
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| A109024 |
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4-almost primes (A014613) whose digit reversal is different and also has 4 prime factors (with multiplicity). "Emirp Tsolma-4.". |
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11
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| 126, 225, 294, 315, 459, 488, 492, 513, 522, 558, 621, 650, 738, 837, 855, 884, 954, 1035, 1062, 1098, 1107, 1197, 1206, 1236, 1287, 1305, 1422, 1518, 1617, 1665, 1917, 1926, 1956, 1962, 1989, 2004, 2034, 2046, 2068, 2104, 2148, 2170, 2180, 2223, 2226
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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This sequence is the k = 4 instance of the series which begins with k = 1 (emirps), k = 2 (emirpimes), k = 3 (emirp tsolma-3 = A109023).
The Mathematica code for this was written by Ray Chandler who extended this sequence. He also has more values.
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REFERENCES
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Jonathan Vos Post, "1066 and All That: Emirp Tsolma-3 and Related Integer Sequences." Forthcoming paper on this sequence.
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LINKS
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Eric Weisstein's World of Mathematics, Almost Prime.
Eric Weisstein's World of Mathematics, Emirp.
Eric Weisstein and Jonathan Vos Post, Emirpimes.
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EXAMPLE
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a(1) = 126 is in this sequence because 126 = 2 * 3^2 * 7 is a 4-almost prime and reverse(126) = 621 = 3^3 * 23 is also a 4-almost prime.
a(2) = 225 is in this sequence because 225 = 3^2 * 5^2 is a 4-almost prime and reverse(225) = 522 = 2 * 3^2 * 29 is also a 4-almost prime. That 225 and 522 are concatenated from entirely prime digits is a coincidence, as with 2223).
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CROSSREFS
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Cf. A006567, A097393, A109018, A109023, A109025-A109131.
Sequence in context: A020342 A009944 A104395 this_sequence A063334 A102805 A135192
Adjacent sequences: A109021 A109022 A109023 this_sequence A109025 A109026 A109027
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KEYWORD
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nonn,base
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Jun 16 2005
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