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%I #30 Aug 06 2021 03:53:34
%S 0,0,12,200,2660,31850,361985,3982799,42914655,455727689,4788989458,
%T 49930700093,517443017072,5336861879564
%N Number of positive integers with n digits that are the product of two integers greater than 1 and ending with 1.
%C a(n) is the number of n-digit numbers in A346507.
%F Conjecture: Lim_{n->infinity} a(n)/a(n-1) = 10.
%o (Python)
%o def A346507upto(lim): return sorted(set(a*b for a in range(11, lim//11+1, 10) for b in range(a, lim//a+1, 10)))
%o def a(n): return len(A346507upto(10**n)) - len(A346507upto(10**(n-1)))
%o print([a(n) for n in range(1, 9)]) # _Michael S. Branicky_, Jul 22 2021
%o (PARI) a(n) = {my(res = 0); forstep(i = 10^(n-1) + 1, 10^n, 10, f = factor(i); if(bigomega(f) == 1, next); d = divisors(f); for(j = 2, (#d~ + 1)>>1, if(d[j]%10 == 1 && d[#d + 1 - j]%10 == 1, res++; next(2) ) ) ); res } \\ _David A. Corneth_, Jul 22 2021
%Y Cf. A017281, A052268, A087630, A337855 (ending with 5), A337856 (ending with 6), A346507.
%K nonn,base,hard,more
%O 1,3
%A _Stefano Spezia_, Jul 21 2021
%E a(6)-a(9) from _Michael S. Branicky_, Jul 22 2021
%E a(10) from _David A. Corneth_, Jul 22 2021
%E a(11) from _Michael S. Branicky_, Jul 23 2021
%E a(11) corrected and extended with a(12) by _Martin Ehrenstein_, Aug 03 2021
%E a(13)-a(14) from _Martin Ehrenstein_, Aug 05 2021
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