A085248 Left truncatable 3-almost primes, in which repeatedly deleting the leftmost digit gives a 3-almost prime at every step until a single-digit 3-almost prime remains.

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

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: A017365 A352735 A084394 * A278546 A092163 A100592

Adjacent sequences: A085245 A085246 A085247 * A085249 A085250 A085251

Keyword

nonn,base

Author

Shyam Sunder Gupta, Aug 11 2003

Status

approved