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Search: id:A135355
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| A135355 |
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Semiprimes with digits in ascending order. |
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+0
1
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| 4, 6, 9, 14, 15, 25, 26, 34, 35, 38, 39, 46, 49, 57, 58, 69, 123, 129, 134, 145, 146, 158, 159, 169, 178, 235, 237, 247, 249, 259, 267, 278, 289, 346, 358, 458, 469, 478, 489, 579, 589, 679, 689, 789, 1234, 1238, 1247, 1257, 1267, 1345, 1346, 1347, 1349, 1357
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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This is to A028864 as A001358 is to A000040. Semiprime metadromes in base 10. Contains 175 entries, the last being a(175)=12345789 = 3 * 4115263 .
Snapshots: a(100)=13579, a(150)=135689, a(160)=245678, a(163)=356789, a(169)=1346789, a(173)=2356789. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 11 2007
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LINKS
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R. J. Mathar, Table of n, a(n) for n = 1..175
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FORMULA
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Equals A001358 INTERSECT A009993. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 11 2007
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MAPLE
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isA001358 := proc(n) if numtheory[bigomega](n) = 2 then true; else false ; fi ; end: isA009993 := proc(n) local dgs, i ; dgs := convert(n, base, 10) ; if nops(dgs) = 1 then RETURN(true) ; fi ; for i from 1 to nops(dgs)-1 do if op(i, dgs) <= op(i+1, dgs) then RETURN(false) ; fi ; od: RETURN(true) ; end: isA135355 := proc(n) isA001358(n) and isA009993(n) ; end: for n from 4 to 1400 do if isA135355(n) then printf("%d, ", n) ; fi ; od: - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 11 2007
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CROSSREFS
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Cf. A001358, A028864.
Adjacent sequences: A135352 A135353 A135354 this_sequence A135356 A135357 A135358
Sequence in context: A120134 A112381 A108634 this_sequence A050940 A084336 A094750
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KEYWORD
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base,easy,fini,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Dec 08 2007
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EXTENSIONS
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Corrected by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 11 2007
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