A038481 Sums of 2 distinct powers of 7.

8, 50, 56, 344, 350, 392, 2402, 2408, 2450, 2744, 16808, 16814, 16856, 17150, 19208, 117650, 117656, 117698, 117992, 120050, 134456, 823544, 823550, 823592, 823886, 825944, 840350, 941192, 5764802, 5764808, 5764850, 5765144, 5767202

Offset

0,1

Links

Robert Israel, Table of n, a(n) for n = 0..10010

Formula

G.f.: ((1-x)*(1-7*x))^(-1) * (2 - 8*x + sum_{k>=0} ((1+5*7^k)*x^(k*(k+1)/2) + (1+41*7^k)*x^(1+k*(k+1)/2))). - Robert Israel, Feb 09 2018

Maple

seq(seq(7^i+7^j, j=0..i-1), i=1..10); # Robert Israel, Feb 09 2018

Mathematica

Sort[Total/@Subsets[7^Range[0, 10], {2}]] (* Harvey P. Dale, Jul 29 2015 *)

Prog

(Python)
from math import isqrt
def A038481(n): return 7**(m:=isqrt(n<<3)+1>>1)+7**(n-1-(m*(m-1)>>1)) # Chai Wah Wu, Apr 05 2025

Crossrefs

Base 7 interpretation of A038444.

Sequence in context: A299125 A299883 A043398 * A043015 A076286 A299049

Adjacent sequences: A038478 A038479 A038480 * A038482 A038483 A038484

Keyword

nonn,easy

Author

Olivier Gérard

Status

approved