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%I #16 Nov 13 2023 14:53:51
%S 9,39,69,99,129,159,169,189,219,249,279,299,309,339,369,399,429,459,
%T 489,519,529,549,559,579,609,639,669,689,699,729,759,789,819,849,879,
%U 909,939,949,969,989,999,1029,1059,1079,1089,1119,1149,1179,1209,1219,1239,1269
%N Positive integers k that are the product of two integers ending with 3.
%C All the terms end with 9 (A017377).
%H Stefano Spezia, <a href="/A346950/b346950.txt">Table of n, a(n) for n = 1..10000</a>
%F Limit_{n->oo} a(n)/a(n-1) = 1.
%e 9 = 3*3, 39 = 3*13, 69 = 3*23, 99 = 3*33, 129 = 3*43, 159 = 3*53, 169 = 13*13, 189 = 3*63, ...
%t a={}; For[n=0, n<=250, n++, For[k=0, k<=n, k++, If[Mod[10*n+9, 10*k+3]==0 && Mod[(10*n+9)/(10*k+3), 10]==3&& 10*n+9>Max[a], AppendTo[a, 10*n+9]]]]; a
%o (Python)
%o def aupto(lim): return sorted(set(a*b for a in range(3, lim//3+1, 10) for b in range(a, lim//a+1, 10)))
%o print(aupto(1270)) # _Michael S. Branicky_, Aug 08 2021
%Y Cf. A017377 (supersequence), A053742 (ending with 5), A139245 (ending with 2), A324297 (ending with 6), A346951, A346952, A346953.
%K nonn,base
%O 1,1
%A _Stefano Spezia_, Aug 08 2021
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