A038479 Sums of 3 distinct powers of 6.

43, 223, 253, 258, 1303, 1333, 1338, 1513, 1518, 1548, 7783, 7813, 7818, 7993, 7998, 8028, 9073, 9078, 9108, 9288, 46663, 46693, 46698, 46873, 46878, 46908, 47953, 47958, 47988, 48168, 54433, 54438, 54468, 54648, 55728, 279943, 279973, 279978, 280153, 280158, 280188

Offset: 1

Author

Olivier Gérard

Keywords

• nonn
• easy

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Base-6 interpretation of A038445.

Cf. A000400, A038478, A038480.

Programs

Maple

N:= 9: # to get all terms < 6^(N+1)
seq(seq(seq(6^i+6^j+6^k,k=0..j-1),j=1..i-1),i=2..N);

Mathematica

Union[Total/@Subsets[6^Range[0,8],{3}]] (* Harvey P. Dale, May 17 2011 *)

Python

from math import isqrt, comb
from sympy import integer_nthroot
def A038479(n): return 6**((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))+6**((a:=isqrt(s:=n-comb(m-(t^1)+2,3)<<1))+((s<<2)>(a<<2)*(a+1)+1))+6**(m+t+1) # Chai Wah Wu, Apr 05 2025

Extensions

Offset changed by Robert Israel, May 08 2018