A269503 Largest prime factor of A138148(n).

101, 13, 137, 9091, 9901, 909091, 5882353, 52579, 333667, 9091, 99990001, 1058313049, 265371653, 909091, 2906161, 21993833369, 999999000001, 909090909090909091, 1111111111111111111, 909091, 1056689261, 549797184491917, 11111111111111111111111

Offset

1,1

Comments

Largest prime factor of (10^(n+1)+1)*(10^n-1)/9.

Links

Max Alekseyev, Table of n, a(n) for n = 1..344

Formula

a(n) = max(A003020(n),A003021(n+1)) for n >= 2. - Robert Israel, May 11 2016

Example

a(4) = 9091 because largest prime factor of 111101111 is 9091.

Maple

seq(max(max(numtheory:-factorset((10^n-1)/9)),
max(numtheory:-factorset(10^(n+1)+1))), n=1..30); # Robert Israel, May 11 2016

Prog

(PARI) a006530(n) = if(n>1, vecmax(factor(n)[, 1]), 1);
for(n=1, 25, print1(a006530((10^(2*n+1)-1)/9-10^n), ", "));

Crossrefs

Cf. A003020, A003021, A006530, A138148.

Sequence in context: A288896 A290291 A267511 * A067748 A338615 A190757

Adjacent sequences: A269500 A269501 A269502 * A269504 A269505 A269506

Keyword

nonn

Author

Altug Alkan, May 11 2016

Status

approved