A347748 Number of positive integers with n digits that are equal both to the product of two integers ending with 4 and to that of two integers ending with 6.
0, 1, 12, 159, 1859, 20704, 223525, 2370684, 24842265, 258128126, 2665475963
Offset: 1
Programs
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Mathematica
Table[{lo, hi}={10^(n-1), 10^n}; Length@Select[Intersection[Union@Flatten@Table[a*b, {a, 4, Floor[hi/4], 10}, {b, a, Floor[hi/a], 10}],Union@Flatten@Table[a*b, {a, 6, Floor[hi/6], 10}, {b, a, Floor[hi/a], 10}]], lo<# -
Python
def a(n): lo, hi = 10**(n-1), 10**n 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) & set(a*b for a in range(6, hi//6+1, 10) for b in range(a, hi//a+1, 10) if lo <= a*b < hi)) print([a(n) for n in range(1, 9)]) # Michael S. Branicky, Oct 06 2021
Formula
Extensions
a(9)-a(10) from Michael S. Branicky, Oct 06 2021
a(11) from Frank A. Stevenson, Jan 06 2024
Comments