OFFSET
0,2
COMMENTS
This is equivalent to changing decimal digits 0,1,..,9 to base 100 digits 0,11,..,99, so the sequence is numbers which can be written in base 100 using only digits 0,11,..,99. Also, numbers whose decimal digit runs are all even lengths (including 0 as no digits at all).
LINKS
Kevin Ryde, Table of n, a(n) for n = 0..10000
FORMULA
a(n) = Sum_{i=0..k} 11*d[i]*100^i where the decimal expansion of n is n = Sum_{i=0..k} d[i]*10^i with digits 0 <= d[i] <= 9.
a(n) = A051022(n)*11 for n > 0. - Kritsada Moomuang, Oct 20 2019
EXAMPLE
For n=5517, digits duplicate to a(n) = 55551177.
PROG
(PARI) a(n) = fromdigits(digits(n), 100)*11;
(Python)
def A338754(n): return int(''.join(d*2 for d in str(n))) # Chai Wah Wu, May 07 2022
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Kevin Ryde, Nov 06 2020
STATUS
approved