21150551 has 4 divisors (see below), whose sum is σ = 21549672. Its totient is φ = 20751432.

The previous prime is 21150523. The next prime is 21150607. The reversal of 21150551 is 15505112.

It is a happy number.

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 21150551 - 2⁶ = 21150487 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 (21153551) 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, 199481 + ... + 199586.

It is an arithmetic number, because the mean of its divisors is an integer number (5387418).

Almost surely, 2^21150551 is an apocalyptic number.

21150551 is a deficient number, since it is larger than the sum of its proper divisors (399121).

21150551 is an equidigital number, since it uses as much as digits as its factorization.

21150551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 399120.

The product of its (nonzero) digits is 250, while the sum is 20.

The square root of 21150551 is about 4598.9728200980. The cubic root of 21150551 is about 276.5501480285.

Adding to 21150551 its product of nonzero digits (250), we get a square (21150801 = 4599²).

Adding to 21150551 its reverse (15505112), we get a palindrome (36655663).

The spelling of 21150551 in words is "twenty-one million, one hundred fifty thousand, five hundred fifty-one".