21987899 has 2 divisors, whose sum is σ = 21987900. Its totient is φ = 21987898.

The previous prime is 21987871. The next prime is 21987907. The reversal of 21987899 is 99878912.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21987899 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21987899.

It is not a weakly prime, because it can be changed into another prime (21987809) 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, 10993949 + 10993950.

It is an arithmetic number, because the mean of its divisors is an integer number (10993950).

Almost surely, 2^21987899 is an apocalyptic number.

21987899 is a deficient number, since it is larger than the sum of its proper divisors (1).

21987899 is an equidigital number, since it uses as much as digits as its factorization.

21987899 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 653184, while the sum is 53.

The square root of 21987899 is about 4689.1256114547. The cubic root of 21987899 is about 280.1525486766.

The spelling of 21987899 in words is "twenty-one million, nine hundred eighty-seven thousand, eight hundred ninety-nine".