A046468 Numbers k such that the concatenation of numbers from 1 to k is the product of 9 primes (not necessarily distinct).

26, 36, 40, 52, 74, 90, 102, 112, 114, 115

Offset

1,1

Links

Table of n, a(n) for n=1..10.

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[52], PrimeOmega[FromDigits[Flatten[IntegerDigits/@ Range[ #]]]] ==9&] (* Harvey P. Dale, Nov 12 2017 *)

Crossrefs

Cf. A046460.

Sequence in context: A291158 A326733 A103079 * A138065 A240897 A034096

Adjacent sequences: A046465 A046466 A046467 * A046469 A046470 A046471

Keyword

nonn,base,hard,more,less

Author

Patrick De Geest, Aug 15 1998

Extensions

a(5)-a(10) from Sean A. Irvine, Apr 10 2021

Status

approved