A046466 Numbers k such that the concatenation of numbers from 1 to k is the product of 7 primes (not necessarily distinct).

28, 30, 42, 44, 46, 69, 72, 82, 84, 86, 93, 109, 116

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@# == 7 &] (* Robert Price, Oct 11 2019 *)

Crossrefs

Cf. A046460.

Sequence in context: A042621 A042622 A044977 * A374008 A054396 A083274

Adjacent sequences: A046463 A046464 A046465 * A046467 A046468 A046469

Keyword

nonn,base,hard,more

Author

Patrick De Geest, Aug 15 1998

Extensions

a(6)-a(13) from Sean A. Irvine, Apr 10 2021

Status

approved