21263621 has 2 divisors, whose sum is σ = 21263622. Its totient is φ = 21263620.

The previous prime is 21263587. The next prime is 21263623. The reversal of 21263621 is 12636212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20340100 + 923521 = 4510^2 + 961^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21263621 is a prime.

Together with 21263623, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21263623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10631810 + 10631811.

It is an arithmetic number, because the mean of its divisors is an integer number (10631811).

Almost surely, 2^21263621 is an apocalyptic number.

It is an amenable number.

21263621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21263621 is an equidigital number, since it uses as much as digits as its factorization.

21263621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 864, while the sum is 23.

The square root of 21263621 is about 4611.2493968555. The cubic root of 21263621 is about 277.0420811270.

Adding to 21263621 its reverse (12636212), we get a palindrome (33899833).

The spelling of 21263621 in words is "twenty-one million, two hundred sixty-three thousand, six hundred twenty-one".