OFFSET
1,2
COMMENTS
Numbers of the form (4^i - 4^j)/3 with i > j.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
336 = 4^2 + 4^3 + 4^4, so 336 is in the sequence.
+------+--------+
| a(n) | base 4*|
+------+--------+
| 1 | 1 |
| 4 | 10 |
| 5 | 11 |
| 16 | 100 |
| 20 | 110 |
| 21 | 111 |
| 64 | 1000 |
| 80 | 1100 |
| 84 | 1110 |
| 85 | 1111 |
+------+--------+
* - a(n) written in base 4.
MATHEMATICA
Module[{nn=10, k}, k=4^Range[0, nn]; Table[Accumulate[Reverse[Take[k, n]]], {n, nn}]]//Flatten (* Harvey P. Dale, May 29 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Aug 15 2019
STATUS
approved