21525861 has 32 divisors (see below), whose sum is σ = 35094528. Its totient is φ = 11468160.

The previous prime is 21525857. The next prime is 21525883. The reversal of 21525861 is 16852512.

It is not a de Polignac number, because 21525861 - 2² = 21525857 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21525061) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 19260 + ... + 20346.

It is an arithmetic number, because the mean of its divisors is an integer number (1096704).

Almost surely, 2^21525861 is an apocalyptic number.

21525861 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21525861 is a deficient number, since it is larger than the sum of its proper divisors (13568667).

21525861 is a wasteful number, since it uses less digits than its factorization.

21525861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1161.

The product of its digits is 4800, while the sum is 30.

The square root of 21525861 is about 4639.5970730226. The cubic root of 21525861 is about 278.1763325863.

It can be divided in two parts, 21525 and 861, that multiplied together give a square (18533025 = 4305²).

The spelling of 21525861 in words is "twenty-one million, five hundred twenty-five thousand, eight hundred sixty-one".