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A055237
Sums of two powers of 5.
7
2, 6, 10, 26, 30, 50, 126, 130, 150, 250, 626, 630, 650, 750, 1250, 3126, 3130, 3150, 3250, 3750, 6250, 15626, 15630, 15650, 15750, 16250, 18750, 31250, 78126, 78130, 78150, 78250, 78750, 81250, 93750, 156250, 390626, 390630, 390650, 390750, 391250, 393750
OFFSET
0,1
LINKS
Michael Penn, Fives and squares., YouTube video, 2021.
FORMULA
a(n) = 5^(n-trinv(n))+5^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) = 5^n + 5^k, so as a sequence a(n) = 5^A002262(n) + 5^A003056(n).
MATHEMATICA
t = 5^Range[0, 9]; Select[Union[Flatten[Table[i + j, {i, t}, {j, t}]]], # <= t[[-1]] + 1 &] (* T. D. Noe, Oct 09 2011 *)
Total/@Tuples[5^Range[0, 9], 2]//Union (* Harvey P. Dale, Jan 29 2017 *)
CROSSREFS
Cf. A052216.
Sequence in context: A258143 A369290 A079713 * A057434 A333170 A217381
KEYWORD
nonn,easy,tabl
AUTHOR
Henry Bottomley, Jun 22 2000
STATUS
approved