21261813 has 16 divisors (see below), whose sum is σ = 29258496. Its totient is φ = 13726400.

The previous prime is 21261811. The next prime is 21261827. The reversal of 21261813 is 31816212.

It is a cyclic number.

It is not a de Polignac number, because 21261813 - 2¹ = 21261811 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21261811) 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, 13495 + ... + 14987.

It is an arithmetic number, because the mean of its divisors is an integer number (1828656).

Almost surely, 2^21261813 is an apocalyptic number.

It is an amenable number.

21261813 is a deficient number, since it is larger than the sum of its proper divisors (7996683).

21261813 is a wasteful number, since it uses less digits than its factorization.

21261813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1644.

The product of its digits is 576, while the sum is 24.

The square root of 21261813 is about 4611.0533503745. The cubic root of 21261813 is about 277.0342288068.

The spelling of 21261813 in words is "twenty-one million, two hundred sixty-one thousand, eight hundred thirteen".