A002243 Numbers that are not the sum of 3 distinct triangular numbers.
1, 2, 3, 5, 6, 8, 12, 15, 20, 23, 33, 78
Offset: 1
Programs
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Mathematica
Complement[Range[100],Union[Total/@Subsets[Accumulate[Range[0,12]], {3}]]] (* Harvey P. Dale, Sep 02 2014 *) -
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 select(is,[1..100]) \\ Charles R Greathouse IV, Nov 25 2014