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A337856 Number of positive integers with n digits that are the product of two integers ending with 6.

%I A337856 #28 Sep 26 2021 10:36:59
%S A337856 0,2,20,230,2515,26889,282211,2930013,30196730,309564822,3161099901,
%T A337856 32182595954,326874672928,3313770788984
%N A337856 Number of positive integers with n digits that are the product of two integers ending with 6.
%C A337856 a(n) is the number of n-digit numbers in A324297.
%H A337856 <a href="/index/Di#digits">Index entries for sequences related to digits</a>.
%F A337856 Conjecture: Lim_{n->infinity} a(n)/a(n-1) = 10.
%o A337856 (Python)
%o A337856 def A337856(n):
%o A337856     k, n1, n2, pset = 0, 10**(n-1)//2-18, 10**n//2-18, set()
%o A337856     while 50*k**2+60*k < n2:
%o A337856         a, b = divmod(n1-30*k,50*k+30)
%o A337856         m = max(k,a+int(b>0))
%o A337856         r = 50*k*m+30*(k+m)
%o A337856         while r < n2:
%o A337856             pset.add(r)
%o A337856             m += 1
%o A337856             r += 50*k+30
%o A337856         k += 1
%o A337856     return len(pset) # _Chai Wah Wu_, Sep 26 2021
%Y A337856 Cf. A017341, A324297, A337855, A346509.
%K A337856 nonn,base,hard,more
%O A337856 1,2
%A A337856 _Stefano Spezia_, Sep 27 2020
%E A337856 a(5) corrected by and a(6)-a(9) from _Jinyuan Wang_, Oct 01 2020
%E A337856 a(10)-a(13) from _Bert Dobbelaere_, Oct 20 2020
%E A337856 a(14) from _Martin Ehrenstein_, Aug 06 2021