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%I #17 Jul 06 2019 00:45:43
%S 0,1,3,8,20,34
%N The indices of tetrahedral numbers that are also triangular.
%H E. T. Avanesov, <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa12/aa12128.pdf">Solution of a problem on figurate numbers</a> (in Russian), Acta Arith. 12 1966/1967 pages 409-420.
%e The eighth tetrahedral number is 120, which is also a triangular number. Hence, 8 belongs to the sequence.
%o (PARI) for(n=0,34,if(ispolygonal(n*(n+1)*(n+2)/6,3),print1(n", "))) \\ _Charles R Greathouse IV_, Apr 07 2013
%Y Cf. A027568, A102349.
%K nonn,full,fini
%O 0,3
%A _Tanya Khovanova_, Apr 06 2013
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