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A055258
Sums of two powers of 7.
6
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
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
KEYWORD
easy,nonn,tabl
AUTHOR
Henry Bottomley, Jun 22 2000
STATUS
approved