21993553 has 4 divisors (see below), whose sum is σ = 22151920. Its totient is φ = 21835188.

The previous prime is 21993541. The next prime is 21993581. The reversal of 21993553 is 35539912.

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 21993553 - 2¹³ = 21985361 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21993593) 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, 78975 + ... + 79252.

It is an arithmetic number, because the mean of its divisors is an integer number (5537980).

Almost surely, 2^21993553 is an apocalyptic number.

It is an amenable number.

21993553 is a deficient number, since it is larger than the sum of its proper divisors (158367).

21993553 is a wasteful number, since it uses less digits than its factorization.

21993553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 158366.

The product of its digits is 36450, while the sum is 37.

The square root of 21993553 is about 4689.7284569578. The cubic root of 21993553 is about 280.1765595618.

The spelling of 21993553 in words is "twenty-one million, nine hundred ninety-three thousand, five hundred fifty-three".