21715553 has 4 divisors (see below), whose sum is σ = 21871920. Its totient is φ = 21559188.

The previous prime is 21715541. The next prime is 21715621. The reversal of 21715553 is 35551712.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21715553 - 2⁶ = 21715489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21715153) 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, 77975 + ... + 78252.

It is an arithmetic number, because the mean of its divisors is an integer number (5467980).

Almost surely, 2^21715553 is an apocalyptic number.

It is an amenable number.

21715553 is a deficient number, since it is larger than the sum of its proper divisors (156367).

21715553 is a wasteful number, since it uses less digits than its factorization.

21715553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 156366.

The product of its digits is 5250, while the sum is 29.

The square root of 21715553 is about 4659.9949570788. The cubic root of 21715553 is about 278.9910669750.

The spelling of 21715553 in words is "twenty-one million, seven hundred fifteen thousand, five hundred fifty-three".