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A046466 Numbers k such that the concatenation of numbers from 1 to k is the product of 7 primes (not necessarily distinct). 1
28, 30, 42, 44, 46 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..5.

Patrick De Geest, Normal Smarandache Concatenated Numbers, Prime factors from 1 up to n

M. Fleuren, Smarandache Factors and Reverse factors

Carlos Rivera, Primes by Listing, The Prime Puzzles & Problems Connection.

MATHEMATICA

Select[Range[100],

PrimeOmega@FromDigits@Flatten@IntegerDigits@Range@# == 7 &] (* Robert Price, Oct 11 2019 *)

CROSSREFS

Cf. A046460.

Sequence in context: A042621 A042622 A044977 * A054396 A083274 A067913

Adjacent sequences:  A046463 A046464 A046465 * A046467 A046468 A046469

KEYWORD

nonn,hard,base

AUTHOR

Patrick De Geest, Aug 15 1998

STATUS

approved

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Last modified September 25 00:02 EDT 2020. Contains 337333 sequences. (Running on oeis4.)