A046464 Numbers k such that the concatenation of numbers from 1 to k is the product of 5 primes (not necessarily distinct).

8, 17, 25, 41, 47, 55, 56, 63, 77, 94, 101, 103, 107

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, Factors and primes of Smarandache sequences.

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@# == 5 &] (* Robert Price, Oct 11 2019 *)

Crossrefs

Cf. A007908, A046460, A050682.

Sequence in context: A118066 A044060 A121283 * A022390 A041831 A041122

Adjacent sequences: A046461 A046462 A046463 * A046465 A046466 A046467

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