OFFSET
0,3
COMMENTS
Inspired by Luhn algorithm for validating credit cards.
FORMULA
a(n) = sum of digits(if n odd then n else 2n).
EXAMPLE
a(11) = 2 = 1 + 1 (1 and 1 are the digits in 11).
a(12) = 6 = 2 + 4 (2 and 4 are the digits in 24 = 2 * 12).
MATHEMATICA
f[n_] := Plus @@ IntegerDigits[ If[ OddQ[n], n, 2n]]; Table[ f[n], {n, 0, 90}] (* Robert G. Wilson v, Mar 24 2004 *)
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Semaphore Corporation (help(AT)semaphorecorp.com), Mar 20 2004
EXTENSIONS
Corrected and extended by Ray Chandler, Mar 21 2004
STATUS
approved