21534638987 has 2 divisors, whose sum is σ = 21534638988. Its totient is φ = 21534638986.

The previous prime is 21534638981. The next prime is 21534638989. The reversal of 21534638987 is 78983643512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21534638987 - 2⁴ = 21534638971 is a prime.

Together with 21534638989, 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 (21534638981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10767319493 + 10767319494.

It is an arithmetic number, because the mean of its divisors is an integer number (10767319494).

Almost surely, 2^21534638987 is an apocalyptic number.

21534638987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21534638987 is an equidigital number, since it uses as much as digits as its factorization.

21534638987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8709120, while the sum is 56.

The spelling of 21534638987 in words is "twenty-one billion, five hundred thirty-four million, six hundred thirty-eight thousand, nine hundred eighty-seven".