21821951 has 4 divisors (see below), whose sum is σ = 21955992. Its totient is φ = 21687912.

The previous prime is 21821929. The next prime is 21821953. The reversal of 21821951 is 15912812.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21821951 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21821953) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66776 + ... + 67101.

It is an arithmetic number, because the mean of its divisors is an integer number (5488998).

Almost surely, 2^21821951 is an apocalyptic number.

21821951 is a deficient number, since it is larger than the sum of its proper divisors (134041).

21821951 is a wasteful number, since it uses less digits than its factorization.

21821951 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 134040.

The product of its digits is 1440, while the sum is 29.

The square root of 21821951 is about 4671.3971143545. The cubic root of 21821951 is about 279.4459750740.

The spelling of 21821951 in words is "twenty-one million, eight hundred twenty-one thousand, nine hundred fifty-one".