A038470 Sums of 2 distinct powers of 4.

5, 17, 20, 65, 68, 80, 257, 260, 272, 320, 1025, 1028, 1040, 1088, 1280, 4097, 4100, 4112, 4160, 4352, 5120, 16385, 16388, 16400, 16448, 16640, 17408, 20480, 65537, 65540, 65552, 65600, 65792, 66560, 69632, 81920, 262145, 262148, 262160, 262208, 262400, 263168

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Mathematica

Sort[Plus @@@ Subsets[4^Range[0, 9], {2}]] (* Amiram Eldar, Jul 13 2022 *)

Prog

(Python)
def aupto(limit):
  p = [4**i for i in range(limit//4+1) if 4**i < limit]
  p2 = set(a+b for i, a in enumerate(p) for b in p[i+1:] if a+b <= limit)
  return sorted(p2)
print(aupto(265000)) # Michael S. Branicky, May 17 2021
(Python)
from math import isqrt
def A038470(n): return (1<<(m:=isqrt(n<<3)+1&-2))+(1<<(n-1<<1)-((k:=m>>1)*(k-1))) # Chai Wah Wu, Apr 05 2025

Crossrefs

Base-4 interpretation of A038444.

Cf. A000302, A038471, A038472, A038473.

Sequence in context: A045119 A045095 A061940 * A043003 A246329 A351176

Adjacent sequences: A038467 A038468 A038469 * A038471 A038472 A038473

Keyword

nonn,easy

Author

Olivier Gérard

Extensions

Offset corrected by Amiram Eldar, Jul 13 2022

Status

approved