OFFSET
0,3
COMMENTS
From a(3) onward the digital root is periodic with period length equal to six: 1,2,4,8,7,5.
EXAMPLE
a(3) = 10 because a(0) + a(1) = 1 and 10 is the minimum number greater than 1 whose digit sum is equal to 1.
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Paolo P. Lava & Giorgio Balzarotti, Jun 24 2009
STATUS
approved