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%I #17 Sep 23 2023 07:29:26
%S 1,3,6,45,210,7140,122265,242556,1702935,8239770,279909630,4601330415,
%T 9508687656,64088265153,323015470680,10973017315470,173166468725253,
%U 372759573255306,2411897769074475,12662852473364940,430164224521152660,6516946879404850395
%N Triangular numbers whose largest proper divisor is also triangular.
%C No more terms < 10^16. - _David Wasserman_, Apr 05 2005
%C 2^63 < a(23) <= 14612920781245825506. - _Donovan Johnson_, Apr 24 2011
%o (PARI) isTriang(n) = local(x); x = sqrtint(2*n); n == x*(x + 1)/2;
%o i = 1; n = 1; print1(n, ", "); while(1, i++; n += i; f = factor(n); if (isTriang(n/f[1, 1]), print1(n, ", "))); \\ _David Wasserman_, Apr 05 2005
%K nonn
%O 1,2
%A _Jason Earls_, Nov 01 2002
%E More terms from _David Wasserman_, Apr 05 2005
%E a(20)-a(22) from _Donovan Johnson_, Apr 24 2011
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