A038465 Sums of 3 distinct powers of 3.

13, 31, 37, 39, 85, 91, 93, 109, 111, 117, 247, 253, 255, 271, 273, 279, 325, 327, 333, 351, 733, 739, 741, 757, 759, 765, 811, 813, 819, 837, 973, 975, 981, 999, 1053, 2191, 2197, 2199, 2215, 2217, 2223, 2269, 2271, 2277, 2295, 2431, 2433, 2439, 2457, 2511, 2917

Offset

1,1

Links

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

Mathematica

Total/@Subsets[3^Range[0, 10], {3}]//Union (* Harvey P. Dale, Jul 10 2017 *)

Prog

(Python)
from math import comb, isqrt
from sympy import integer_nthroot
def A038465(n): return 3**((r:=n-1-comb((m:=integer_nthroot(6*n, 3)[0])+(t:=(n>comb(m+2, 3)))+1, 3))-comb((k:=isqrt(b:=r+1<<1))+(b>k*(k+1)), 2))+3**((a:=isqrt(s:=n-comb(m-(t^1)+2, 3)<<1))+((s<<2)>(a<<2)*(a+1)+1))+3**(m+t+1) # Chai Wah Wu, Apr 04 2025

Crossrefs

Base 3 interpretation of A038445.

Cf. A000244, A038464, A038466, A038467, A038468, A038469.

Sequence in context: A227435 A046414 A023694 * A391006 A103665 A040050

Adjacent sequences: A038462 A038463 A038464 * A038466 A038467 A038468

Keyword

nonn,easy

Author

Olivier Gérard

Extensions

Offset corrected by Amiram Eldar, Jul 13 2022

Status

approved