%I
%S 1,7,8,31,24,8,48,127,80,24,120,63,168,48,99,511,288,80,360,224,98,
%T 120,528,512,624,168,728,735,840,224,960,2047,242,288,49,1215,1368,
%U 360,675,1024,1680,440,1848,1088,324,528,2208,512,2400,624,288,1183,2808,728
%N Smallest k such that the kth triangular number has n^2 as divisor.
%C a(2^k) = 2^(2*k+1)1; a(m)=m^21 and for odd prime powers m;
%C A080983(n)=A000217(a(n)).
%H Reinhard Zumkeller, <a href="/A080982/b080982.txt">Table of n, a(n) for n = 1..1000</a>
%o (Haskell)
%o import Data.List (findIndex)
%o import Data.Maybe (fromJust)
%o a080982 n = (+ 1) $ fromJust $
%o findIndex ((== 0) . (`mod` (n ^ 2))) $ tail a000217_list
%o  _Reinhard Zumkeller_, Mar 23 2013
%Y Cf. A011772.
%K nonn
%O 1,2
%A _Reinhard Zumkeller_, Feb 26 2003
