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%I #2 Mar 30 2012 18:51:34
%S 0,1,-1,1,2,-1,1,2,-1,2,1,2,-1,2,3,1,2,3,2,3,4,1,2,-1,2,2,3,2,1,2,3,2,
%T 3,-1,2,3,1,2,2,2,3,3,2,2,3,1,2,3,2,2,3,2,3,3,3,1,2,2,2,3,2,2,3,3,2,2,
%U 1,2,3,2,2,3,2,2,3,3,2,3,1,2,3,2,3,2,2,3,3,2,2,3,3,1,2,2,2,3,3,2,3,2,2,2,2,3,3,1,2,3,2,3,3,2,2,3,2,2,3,3,3,2,1,2,3
%N Smallest number of distinct triangular numbers which sum to n (or -1 if not possible).
%C 20 is the only case where n>3.
%e a(20)=4 since 20=1+3+6+10, a(21)=1 since 21 is triangular, a(22)=2 since 22=1+21, a(23)=-1 since no combination of distinct triangular numbers sum to 23.
%Y Cf. A000217, A002243, A053614, A061208, A061336.
%K sign
%O 0,5
%A _Henry Bottomley_, Apr 25 2001
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