A028836 Iterated sum of digits of n is a power of 2.
1, 2, 4, 8, 10, 11, 13, 17, 19, 20, 22, 26, 28, 29, 31, 35, 37, 38, 40, 44, 46, 47, 49, 53, 55, 56, 58, 62, 64, 65, 67, 71, 73, 74, 76, 80, 82, 83, 85, 89, 91, 92, 94, 98, 100, 101, 103, 107, 109, 110, 112, 116, 118, 119, 121, 125, 127, 128, 130, 134, 136, 137, 139, 143, 145, 146, 148, 152, 154, 155
Offset: 1
Formula
Conjectures from Colin Barker, Feb 10 2020: (Start)
G.f.: x*(1 + x + 2*x^2 + 4*x^3 + x^4) / ((1 - x)^2*(1 + x)*(1 + x^2)).
a(n) = a(n-1) + a(n-4) - a(n-5) for n>5.
(End)
This g.f. follows from the observation that a(n+4) = a(n)+9 and this holds since the iterated sum of digits of N equals the iterated sum of digits of N+9. - Peter Bala, Feb 10 2020
Extensions
More terms from Scott Lindhurst (ScottL(AT)alumni.princeton.edu)
Checked by Neven Juric (neven.juric(AT)apis-it.hr), Feb 04 2008