21251405 has 16 divisors (see below), whose sum is σ = 30679680. Its totient is φ = 13804992.

The previous prime is 21251401. The next prime is 21251413. The reversal of 21251405 is 50415212.

It is a cyclic number.

It is not a de Polignac number, because 21251405 - 2² = 21251401 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21251401) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15314 + ... + 16643.

It is an arithmetic number, because the mean of its divisors is an integer number (1917480).

Almost surely, 2^21251405 is an apocalyptic number.

It is an amenable number.

21251405 is a deficient number, since it is larger than the sum of its proper divisors (9428275).

21251405 is a wasteful number, since it uses less digits than its factorization.

21251405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31988.

The product of its (nonzero) digits is 400, while the sum is 20.

The square root of 21251405 is about 4609.9246197742. The cubic root of 21251405 is about 276.9890171893.

Adding to 21251405 its reverse (50415212), we get a palindrome (71666617).

The spelling of 21251405 in words is "twenty-one million, two hundred fifty-one thousand, four hundred five".