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A014368
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a(n) = bc, where n = C(b,2)+C(c,1), b>c>=0.
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2
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20, 21, 30, 31, 32, 40, 41, 42, 43, 50, 51, 52, 53, 54, 60, 61, 62, 63, 64, 65, 70, 71, 72, 73, 74, 75, 76, 80, 81, 82, 83, 84, 85, 86, 87, 90, 91, 92, 93, 94, 95, 96, 97, 98, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 1110, 120, 121, 122, 123
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OFFSET
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1,1
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COMMENTS
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The definition means: write n as the highest possible triangular number plus some nonnegative rest (so b is one plus the index of the greedy inverse of n in A000217), and concatenate the two decimal expansions of b and the rest. - R. J. Mathar, May 25 2023
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REFERENCES
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W. Bruns and J. Herzog, Cohen-Macaulay Rings, Cambridge, 1993, p. 158.
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LINKS
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MAPLE
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invA000217 := proc(n)
local i;
for i from 1 do
if binomial(i+1, 2) > n then
return i;
end if;
end do:
end proc:
local b, c;
b := invA000217(n) ;
c := n-binomial(b, 2) ;
digcatL([b, c]) ;
end proc:
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CROSSREFS
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KEYWORD
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nonn,easy,base
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AUTHOR
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STATUS
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approved
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