21551518 has 4 divisors (see below), whose sum is σ = 32327280. Its totient is φ = 10775758.

The previous prime is 21551503. The next prime is 21551539. The reversal of 21551518 is 81515512.

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

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5387878 + ... + 5387881.

It is an arithmetic number, because the mean of its divisors is an integer number (8081820).

Almost surely, 2^21551518 is an apocalyptic number.

21551518 is a deficient number, since it is larger than the sum of its proper divisors (10775762).

21551518 is a wasteful number, since it uses less digits than its factorization.

21551518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10775761.

The product of its digits is 2000, while the sum is 28.

The square root of 21551518 is about 4642.3612526386. The cubic root of 21551518 is about 278.2868095673.

The spelling of 21551518 in words is "twenty-one million, five hundred fifty-one thousand, five hundred eighteen".