A347255 - OEIS

%I #16 Sep 29 2021 04:02:15

%S 0,3,25,281,2941,30596,315385,3231664,32972224,335346193,3402373313,

%T 34454358909,348373701706,3518101287286,35491654274101

%N Number of positive integers with n digits that are the product of two integers ending with 4.

%C a(n) is the number of n-digit numbers in A347253.

%F a(n) < A052268(n).

%F Conjecture: lim_{n->infinity} a(n)/a(n-1) = 10.

%o (Python)

%o def a(n):

%o   lo, hi = 10**(n-1), 10**n

%o   return len(set(a*b for a in range(4, hi//4+1, 10) for b in range(a, hi//a+1, 10) if lo <= a*b < hi))

%o print([a(n) for n in range(1, 9)]) # _Michael S. Branicky_, Aug 24 2021

%Y Cf. A017341, A052268, A347253.

%Y Cf. A346509 (ending with 1), A346952 (ending with 3), A337855 (ending with 5), A337856 (ending with 6).

%K nonn,base,hard,more

%O 1,2

%A _Stefano Spezia_, Aug 24 2021

%E a(9)-a(11) from _Michael S. Branicky_, Aug 25 2021

%E a(12)-a(15) from _Martin Ehrenstein_, Sep 29 2021