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A085248 Left truncatable 3-almost primes, in which repeatedly deleting the leftmost digit gives a 3-almost at every step until a single digit 3-almost prime remains. 1
8, 18, 28, 68, 78, 98, 268, 318, 418, 428, 498, 518, 578, 598, 618, 628, 668, 678, 978, 1268, 1498, 1578, 1598, 1978, 2318, 2428, 2598, 2678, 3428, 3598, 3628, 3678, 4318, 4418, 4498, 4978, 5518, 5618, 5678, 6268, 6428, 6618, 6628, 6668, 6978, 7498, 7598 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Terms cannot contain any zero digit. [Harvey P. Dale, Dec 28 2011]

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..600

I. O. Angell and H. J. Godwin, On Truncatable Primes, Math. Comput. 31, 265-267, 1977.

Index entries for sequences related to truncatable primes

EXAMPLE

a(7)=268 is a term because 268,68 and 8 are all 3-almost primes.

MATHEMATICA

lt3pQ[n_]:=Module[{idn=IntegerDigits[n]}, FreeQ[idn, 0]&&Union[ PrimeOmega/@ (FromDigits/@Table[Take[idn, -i], {i, Length[idn]}])] =={3}]; Select[Range[8000], lt3pQ] (* Harvey P. Dale, Dec 28 2011 *)

CROSSREFS

Sequence in context: A277595 A017365 A084394 * A278546 A092163 A100592

Adjacent sequences:  A085245 A085246 A085247 * A085249 A085250 A085251

KEYWORD

nonn,base

AUTHOR

Shyam Sunder Gupta, Aug 11 2003

STATUS

approved

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Last modified February 21 01:15 EST 2019. Contains 320364 sequences. (Running on oeis4.)