21620551 has 4 divisors (see below), whose sum is σ = 21642400. Its totient is φ = 21598704.

The previous prime is 21620531. The next prime is 21620561. The reversal of 21620551 is 15502612.

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-21620551 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 (21620531) 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, 9366 + ... + 11443.

It is an arithmetic number, because the mean of its divisors is an integer number (5410600).

Almost surely, 2^21620551 is an apocalyptic number.

21620551 is a deficient number, since it is larger than the sum of its proper divisors (21849).

21620551 is a wasteful number, since it uses less digits than its factorization.

21620551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21848.

The product of its (nonzero) digits is 600, while the sum is 22.

The square root of 21620551 is about 4649.7904253848. The cubic root of 21620551 is about 278.5836254389.

The spelling of 21620551 in words is "twenty-one million, six hundred twenty thousand, five hundred fifty-one".