A038482 Sums of 3 distinct powers of 7.
57, 351, 393, 399, 2409, 2451, 2457, 2745, 2751, 2793, 16815, 16857, 16863, 17151, 17157, 17199, 19209, 19215, 19257, 19551, 117657, 117699, 117705, 117993, 117999, 118041, 120051, 120057, 120099, 120393, 134457, 134463, 134505, 134799, 136857, 823551, 823593
Offset: 1
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
Union[Total/@Subsets[7^Range[0,10],{3}]] (* Harvey P. Dale, May 06 2014 *) -
Python
from math import isqrt, comb from sympy import integer_nthroot def A038482(n): return 7**((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))+7**((a:=isqrt(s:=n-comb(m-(t^1)+2,3)<<1))+((s<<2)>(a<<2)*(a+1)+1))+7**(m+t+1) # Chai Wah Wu, Apr 05 2025
Extensions
Offset corrected by Amiram Eldar, Jul 14 2022