A135355 - OEIS

A135355

Semiprimes with digits in ascending order.

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

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OFFSET

1,1

COMMENTS

This is to A028864 as A001358 is to A000040. Semiprime metadromes in base 10. Contains 175 terms, 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, Dec 11 2007

LINKS

R. J. Mathar, Table of n, a(n) for n = 1..175

FORMULA

Equals A001358 INTERSECT A009993. - R. J. Mathar, Dec 11 2007

MAPLE

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, Dec 11 2007

CROSSREFS

Cf. A001358, A028864.

Sequence in context: A112381 A182150 A108634 * A350069 A245383 A050940

Adjacent sequences: A135352 A135353 A135354 * A135356 A135357 A135358

KEYWORD

base,easy,fini,nonn

AUTHOR

Jonathan Vos Post, Dec 08 2007

EXTENSIONS

Corrected by R. J. Mathar, Dec 11 2007

STATUS

approved