A055258 Sums of two powers of 7.

2, 8, 14, 50, 56, 98, 344, 350, 392, 686, 2402, 2408, 2450, 2744, 4802, 16808, 16814, 16856, 17150, 19208, 33614, 117650, 117656, 117698, 117992, 120050, 134456, 235298, 823544, 823550, 823592, 823886, 825944, 840350, 941192, 1647086, 5764802, 5764808

Offset

0,1

Links

T. D. Noe, Rows n = 0..100 of triangle, flattened

Formula

a(n) = 7^(n-trinv(n))+7^trinv(n), where trinv(n) = floor((1+sqrt(1+8*n))/2) = A002262(n) and n-trinv(n) = A003056(n)

Regarded as a triangle T(n, k) = 7^n + 7^k, so as a sequence a(n) = 7^A002262(n) + 7^A003056(n).

Mathematica

t = 7^Range[0, 9]; Select[Union[Flatten[Table[i + j, {i, t}, {j, t}]]], # <= t[[-1]] + 1 &] (* T. D. Noe, Oct 09 2011 *)
Total/@Tuples[7^Range[0, 10], 2]//Union (* Harvey P. Dale, Dec 31 2017 *)

Crossrefs

Cf. A052216.

Equals 2*A073218.

Sequence in context: A333054 A119752 A111001 * A277649 A192777 A054981

Adjacent sequences: A055255 A055256 A055257 * A055259 A055260 A055261

Keyword

easy,nonn,tabl

Author

Henry Bottomley, Jun 22 2000

Status

approved