21211387 has 2 divisors, whose sum is σ = 21211388. Its totient is φ = 21211386.

The previous prime is 21211381. The next prime is 21211403. The reversal of 21211387 is 78311212.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21211387 - 2⁷ = 21211259 is a prime.

It is not a weakly prime, because it can be changed into another prime (21211381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605693 + 10605694.

It is an arithmetic number, because the mean of its divisors is an integer number (10605694).

Almost surely, 2^21211387 is an apocalyptic number.

21211387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21211387 is an equidigital number, since it uses as much as digits as its factorization.

21211387 is an evil number, because the sum of its binary digits is even.

The product of its digits is 672, while the sum is 25.

The square root of 21211387 is about 4605.5821564706. The cubic root of 21211387 is about 276.8150441986.

Adding to 21211387 its reverse (78311212), we get a palindrome (99522599).

The spelling of 21211387 in words is "twenty-one million, two hundred eleven thousand, three hundred eighty-seven".