OEIS/A220952
Don Knuth found this sequence "so fascinating":
- 0, 1, 2, 3, 4, 9, 14, 19, 18, 17, 16, 11, 12, 13, 8, 7, 6, 5, 10, 15, 20, 21, 22, 23, 24, 49
I stumbled over it when looking for sequences with keyword unkn
. Here are the values listed in base 5:
n a(n) base 5 0 0 0
1 1 1 2 2 2 3 3 3 4 4 4
5 9 14 6 14 24 7 19 34 8 18 33 9 17 32 10 16 31 11 11 21 12 12 22 13 13 23 14 8 13 15 7 12 16 6 11 17 5 10 18 10 20 19 15 30 20 20 40 21 21 41 22 22 42 23 23 43 24 24 44
25 49 144
Some elementary observations (disregarding the trailing 49):
- A permutation of the numbers 0 ... 24
- a(n=0..12) = 24 - a(24 -n)
- Symmetricy around n=12, a(12) = 2*(5^1 + 5^0)
- Groups of length 5^n - 1, n=0,1,2 ...