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A068821
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Triangular numbers such that both the number formed by the first floor((k+1)/2) digits and the remaining part (if any) are triangular numbers, where k is the number of digits.
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1
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1, 3, 6, 10, 36, 66, 136, 300, 378, 666, 2145, 3655, 10153, 21528, 66066, 78210, 91378, 190036, 210276, 378015, 406351, 630003, 666435, 741153, 946000, 990528, 1537381, 1710325, 3788128, 4652775, 9037626, 87787875
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OFFSET
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1,2
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LINKS
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EXAMPLE
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210276 is a triangular number with k=6 digits and the numbers 210 and 276 are both triangular numbers.
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MAPLE
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filter:= proc(n) local k;
k:= ceil((1+ilog10(n))/2);
issqr(1+8*floor(n/10^k)) and issqr(1+8*(n mod 10^k))
end proc:
select(filter, [seq(i*(i+1)/2, i=1..20000)]); # Robert Israel, Aug 18 2019
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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