0,3

Starting on the right, sum digits after doubling alternating digits beginning with the second. If doubled digit >9, reduce by 9 (sum of digits).

a(n) = A007953(A249873(n); A093019(n) = 10 - a(10*n) mod 10 if less than 10, otherwise 0. - Reinhard Zumkeller, Nov 08 2014

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

John Kilgo, DotNetJohn.com, Using the Luhn Algorithm

Webopedia, Luhn formula

Wikipedia, Luhn algorithm

Index entries for sequences related to decimal expansion of n

a(18) = 2*1 + 8 = 10.

a(59) = (1+0) + 9 = 10 (1 and 0 are the digits in 10 = 2*5).

(Haskell)

a093017 n = if n == 0 then 0 else a093017 n' + a007953 (2 * t) + d

where (n', td) = divMod n 100; (t, d) = divMod td 10

-- Reinhard Zumkeller, Nov 08 2014

Cf. A093018-A093029.

Cf. A007953, A093019.

Sequence in context: A189506 A173529 A273005 * A156230 A028897 A244158

Adjacent sequences: A093014 A093015 A093016 * A093018 A093019 A093020

easy,nonn,base

Ray Chandler, Apr 03 2004

approved