A046467 Numbers k such that the concatenation of numbers from 1 to k is the product of 8 primes (not necessarily distinct).

6, 21, 27, 35, 48, 53, 60, 62, 66, 92, 106, 108, 117

Offset

1,1

Links

Table of n, a(n) for n=1..13.

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

M. Fleuren, Smarandache Factors and Reverse factors

Carlos Rivera, Puzzle 8. Primes by Listing, The Prime Puzzles & Problems Connection.

Mathematica

Select[Range[100], PrimeOmega@FromDigits@Flatten@IntegerDigits@Range@# == 8 &] (* Robert Price, Oct 11 2019 *)

Crossrefs

Cf. A046460.

Sequence in context: A229498 A164698 A020880 * A132184 A143322 A246544

Adjacent sequences: A046464 A046465 A046466 * A046468 A046469 A046470

Keyword

nonn,base,hard,more

Author

Patrick De Geest, Aug 15 1998

Extensions

a(9)-a(13) from Sean A. Irvine, Apr 10 2021

Status

approved