21105861 has 8 divisors (see below), whose sum is σ = 32161344. Its totient is φ = 12060480.

The previous prime is 21105811. The next prime is 21105863. The reversal of 21105861 is 16850112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21105861 - 2¹⁴ = 21089477 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105863) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 502500 + ... + 502541.

It is an arithmetic number, because the mean of its divisors is an integer number (4020168).

Almost surely, 2^21105861 is an apocalyptic number.

21105861 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21105861 is a deficient number, since it is larger than the sum of its proper divisors (11055483).

21105861 is a wasteful number, since it uses less digits than its factorization.

21105861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1005051.

The product of its (nonzero) digits is 480, while the sum is 24.

The square root of 21105861 is about 4594.1115572002. Note that the first 3 decimals coincide. The cubic root of 21105861 is about 276.3552320504.

Adding to 21105861 its reverse (16850112), we get a palindrome (37955973).

It can be divided in two parts, 21 and 105861, that multiplied together give a square (2223081 = 1491²).

The spelling of 21105861 in words is "twenty-one million, one hundred five thousand, eight hundred sixty-one".