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A055258 Sums of two powers of 7. 2
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 (list; table; graph; refs; listen; history; text; internal format)
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

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Last modified October 30 03:24 EDT 2020. Contains 338076 sequences. (Running on oeis4.)