A249873 In decimal representation: replace each even positioned digit with the digit sum of its double.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 30, 31, 32, 33, 34, 35, 36

Offset: 0

Author

Reinhard Zumkeller, Nov 08 2014

Keywords

• nonn
• base

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
• Index entries for sequences related to decimal expansion of n

Crossrefs

Cf. A007953, A093017, A028897.

Programs

Haskell

a249873 n = if n == 0 then 0 else 100*a249873 n' + 10*a007953 (2*t) + d
            where (n', td) = divMod n 100; (t, d) = divMod td 10

PARI

a(n) = my(d=Vecrev(digits(n))); forstep (i=2, #d, 2, d[i] = sumdigits(2*d[i])); fromdigits(Vecrev(d)); \\ Michel Marcus, Jan 23 2022