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A002243
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Numbers that are not the sum of 3 distinct triangular numbers.
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5
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1, 2, 3, 5, 6, 8, 12, 15, 20, 23, 33, 78
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OFFSET
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1,2
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LINKS
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MATHEMATICA
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Complement[Range[100], Union[Total/@Subsets[Accumulate[Range[0, 12]], {3}]]] (* Harvey P. Dale, Sep 02 2014 *)
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PROG
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(PARI) is(n)=for(c=ceil((sqrt(24*n-15)+3)/6), (sqrt(8*n-7)-1)/2, my(t=n-c*(c+1)/2); for(b=sqrtint(t-1)+1, min((sqrt(8*n+1)-1)/2, c-1), if(ispolygonal(t-b*(b+1)/2, 3), return(0)))); 1
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CROSSREFS
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KEYWORD
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fini,full,nonn
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AUTHOR
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STATUS
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approved
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