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A269503 Largest prime factor of A138148(n). 0
101, 13, 137, 9091, 9901, 909091, 5882353, 52579, 333667, 9091, 99990001, 1058313049, 265371653, 909091, 2906161, 21993833369, 999999000001, 909090909090909091, 1111111111111111111, 909091, 1056689261, 549797184491917, 11111111111111111111111 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..23.

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 A190757 A212603

Adjacent sequences:  A269500 A269501 A269502 * A269504 A269505 A269506

KEYWORD

nonn

AUTHOR

Altug Alkan, May 11 2016

STATUS

approved

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Last modified October 20 07:17 EDT 2018. Contains 316378 sequences. (Running on oeis4.)