21987187 has 2 divisors, whose sum is σ = 21987188. Its totient is φ = 21987186.

The previous prime is 21987181. The next prime is 21987197. The reversal of 21987187 is 78178912.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21987187 - 2³ = 21987179 is a prime.

It is not a weakly prime, because it can be changed into another prime (21987181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10993593 + 10993594.

It is an arithmetic number, because the mean of its divisors is an integer number (10993594).

Almost surely, 2^21987187 is an apocalyptic number.

21987187 is a deficient number, since it is larger than the sum of its proper divisors (1).

21987187 is an equidigital number, since it uses as much as digits as its factorization.

21987187 is an evil number, because the sum of its binary digits is even.

The product of its digits is 56448, while the sum is 43.

The square root of 21987187 is about 4689.0496905023. The cubic root of 21987187 is about 280.1495247289.

The spelling of 21987187 in words is "twenty-one million, nine hundred eighty-seven thousand, one hundred eighty-seven".