21373661 has 4 divisors (see below), whose sum is σ = 21395424. Its totient is φ = 21351900.

The previous prime is 21373657. The next prime is 21373691. The reversal of 21373661 is 16637312.

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 21373661 - 2² = 21373657 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 (21373691) 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, 9335 + ... + 11396.

It is an arithmetic number, because the mean of its divisors is an integer number (5348856).

Almost surely, 2^21373661 is an apocalyptic number.

It is an amenable number.

21373661 is a deficient number, since it is larger than the sum of its proper divisors (21763).

21373661 is a wasteful number, since it uses less digits than its factorization.

21373661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21762.

The product of its digits is 4536, while the sum is 29.

The square root of 21373661 is about 4623.1656903036. The cubic root of 21373661 is about 277.5191600006.

The spelling of 21373661 in words is "twenty-one million, three hundred seventy-three thousand, six hundred sixty-one".