OFFSET
1,1
COMMENTS
For n > 8, a(n) = a(n-8) + 11111111, the first 8 values are given in the data.
If n is of the form 3*m+1 then n*10^k-1 is always divisible by 3 but also has a divisor in the set { 11, 73, 101, 137 }.
FORMULA
For n > 8, a(n) = a(n-8) + 11111111.
EXAMPLE
Consider n = 152206.
If k is of the form 2*j+1, n*10^(2*j+1)-1 is divisible by 11.
If k is of the form 8*j, n*10^(8*j)-1 is divisible by 73.
If k is of the form 4*j+2, n*10^(4*j+2)-1 is divisible by 101.
If k is of the form 8*j+4, n*10^(8*j+4)-1 is divisible by 137.
This covers all k, so the covering set is { 11, 73, 101, 137 }.
CROSSREFS
KEYWORD
nonn,easy,changed
AUTHOR
Pierre CAMI, Jul 01 2014
EXTENSIONS
a(9)-a(27) from Jason Yuen, Nov 10 2024
STATUS
approved