21255440387 has 2 divisors, whose sum is σ = 21255440388. Its totient is φ = 21255440386.

The previous prime is 21255440303. The next prime is 21255440389. The reversal of 21255440387 is 78304455212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21255440387 - 2¹⁰ = 21255439363 is a prime.

Together with 21255440389, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21255440389) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10627720193 + 10627720194.

It is an arithmetic number, because the mean of its divisors is an integer number (10627720194).

Almost surely, 2^21255440387 is an apocalyptic number.

21255440387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21255440387 is an equidigital number, since it uses as much as digits as its factorization.

21255440387 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 268800, while the sum is 41.

Adding to 21255440387 its reverse (78304455212), we get a palindrome (99559895599).

The spelling of 21255440387 in words is "twenty-one billion, two hundred fifty-five million, four hundred forty thousand, three hundred eighty-seven".