OFFSET
1,7
EXAMPLE
a(7) = 2 because 2^4 = 16 and 2^10 = 1024 and the sums of the digits of these two numbers are 7; and there are no other numbers like this.
MATHEMATICA
Table[Length[Select[Range[1000], Plus @@ IntegerDigits[2^# ] == n &]], {n, 100}]
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Tanya Khovanova, Dec 13 2006
STATUS
approved