21777621 has 8 divisors (see below), whose sum is σ = 29065344. Its totient is φ = 14504160.

The previous prime is 21777589. The next prime is 21777631. The reversal of 21777621 is 12677712.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21777621 - 2⁵ = 21777589 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21777631) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 745 + ... + 6641.

It is an arithmetic number, because the mean of its divisors is an integer number (3633168).

Almost surely, 2^21777621 is an apocalyptic number.

It is an amenable number.

21777621 is a deficient number, since it is larger than the sum of its proper divisors (7287723).

21777621 is a wasteful number, since it uses less digits than its factorization.

21777621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7131.

The product of its digits is 8232, while the sum is 33.

The square root of 21777621 is about 4666.6498690174. The cubic root of 21777621 is about 279.2566208172.

Subtracting from 21777621 its reverse (12677712), we obtain a palindrome (9099909).

The spelling of 21777621 in words is "twenty-one million, seven hundred seventy-seven thousand, six hundred twenty-one".