

A180927


Largest ndigit number that is divisible by exactly 3 primes (counted with multiplicity).


1



8, 99, 994, 9994, 99997, 999994, 9999994, 99999994, 999999998, 9999999995, 99999999998, 999999999998, 9999999999998, 99999999999998, 999999999999995, 9999999999999998, 99999999999999998, 999999999999999987, 9999999999999999999
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


COMMENTS

This is to 3 and A014612, as 2 and A098450 (largest ndigit semiprime), and as 1 and A003618 (largest ndigit prime). Largest ndigit triprime. Largest ndigit 3almost prime.


LINKS

Table of n, a(n) for n=1..19.


EXAMPLE

a(1) = 8 because 8 = 2^3 is the largest (only) 1digit number that is divisible by exactly 3 primes (counted with multiplicity).
a(2) = 99 because 99 = 3^2 * 11 is the largest 2digit number (of 21) that is divisible by exactly 3 primes (counted with multiplicity).
a(3) = 994 because 994 = 2 * 7 * 71 is the largest 3digit number that is divisible by exactly 3 primes (counted with multiplicity).


MATHEMATICA

lndn3[n_]:=Module[{k=10^n1}, While[PrimeOmega[k]!=3, k]; k]; Array[ lndn3, 20] (* Harvey P. Dale, Jul 25 2019 *)


PROG

(PARI) A180927(n)=forstep(n=10^n1, 10^(n1), 1, bigomega(n)==3&return(n)) \\ M. F. Hasler, Jan 23 2011


CROSSREFS

Cf. A003618, A014612, A098450, A180922.
Sequence in context: A299513 A299313 A300114 * A091801 A050919 A341965
Adjacent sequences: A180924 A180925 A180926 * A180928 A180929 A180930


KEYWORD

nonn,base,easy


AUTHOR

Jonathan Vos Post, Jan 23 2011


STATUS

approved



