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%I #9 Jan 28 2021 10:14:05
%S 1,28,378,4950,59685,699153,7998000,89987820,999961560,1099969156,
%T 11999870821,129999769851,1399999074540,14999999588925,
%U 159999994275696,1699999973850921,17999999979109470,189999999508759300,1999999999000000000,20999999994116393253
%N Largest n-digit triangular number beginning with n.
%o (Python)
%o from sympy import integer_nthroot
%o def a(n):
%o target = 2 * int(str(n) + '9'*(n-len(str(n))))
%o r, exact = integer_nthroot(target, 2)
%o while (r-1)*r//2 <= target//2: r += 1
%o return (r-2)*(r-1)//2
%o print([a(n) for n in range(1, 21)]) # _Michael S. Branicky_, Jan 28 2021
%Y Cf. A000217, A077506 (smallest).
%K base,nonn
%O 1,2
%A _Amarnath Murthy_, Nov 08 2002
%E More terms from _Sascha Kurz_, Jan 04 2003
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