A083889 Number of divisors of n with largest digit = 2 (base 10).

0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 1, 0, 1, 0, 2, 1, 2, 0, 2, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 2, 0, 2, 0, 2, 0, 1, 0, 2, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 3, 0, 1, 1, 1, 0, 2, 0, 1, 0, 1, 0, 2, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 2, 0, 2, 0, 1, 1

Offset: 1

Author

Reinhard Zumkeller, May 08 2003

Keywords

• nonn
• base

Examples

			n=120, 4 of the 16 divisors of 120 have largest digit =2: {2,12,20,120}, therefore a(120)=4.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A054055, A000005, A083897, A083888, A083890, A083891, A083892, A083893, A083894, A083895, A083896, A277964.

Programs

Magma

[#[d:d in Divisors(n) | Max(Intseq(d)) eq 2]: n in [1..120]]; // Marius A. Burtea, Oct 06 2019

Maple

f:= proc(n) nops(select(t -> max(convert(t, base, 10))=d, numtheory:-divisors(n))) end proc:
d:= 2:
map(f, [$1..200]); # Robert Israel, Oct 06 2019

Mathematica

With[{k = 2}, Array[DivisorSum[#, 1 &, And[#[[k]] > 0, Total@ #[[k + 1 ;; 9]] == 0] &@ DigitCount[#] &] &, 105]] (* Michael De Vlieger, Oct 06 2019 *)

Formula

a(n) = A000005(n) - A083888(n) - A083890(n) - A083891(n) - A083892(n) - A083893(n) - A083894(n) - A083895(n) - A083896(n) = A083897(n) - A083888(n).

Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = Sum_{k>=1} 1/A277964(k) = 0.85636382912390578285... . - Amiram Eldar, Jan 04 2024