21918651 has 4 divisors (see below), whose sum is σ = 29224872. Its totient is φ = 14612432.

The previous prime is 21918649. The next prime is 21918667. The reversal of 21918651 is 15681912.

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

It is a cyclic number.

It is not a de Polignac number, because 21918651 - 2¹ = 21918649 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21918601) 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, 3653106 + ... + 3653111.

It is an arithmetic number, because the mean of its divisors is an integer number (7306218).

Almost surely, 2^21918651 is an apocalyptic number.

21918651 is a deficient number, since it is larger than the sum of its proper divisors (7306221).

21918651 is an equidigital number, since it uses as much as digits as its factorization.

21918651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7306220.

The product of its digits is 4320, while the sum is 33.

The square root of 21918651 is about 4681.7358960112. The cubic root of 21918651 is about 279.8581381719.

The spelling of 21918651 in words is "twenty-one million, nine hundred eighteen thousand, six hundred fifty-one".