21911987 has 2 divisors, whose sum is σ = 21911988. Its totient is φ = 21911986.

The previous prime is 21911971. The next prime is 21912013. The reversal of 21911987 is 78911912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21911987 - 2⁴ = 21911971 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21911987.

It is not a weakly prime, because it can be changed into another prime (21911957) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10955993 + 10955994.

It is an arithmetic number, because the mean of its divisors is an integer number (10955994).

Almost surely, 2^21911987 is an apocalyptic number.

21911987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21911987 is an equidigital number, since it uses as much as digits as its factorization.

21911987 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9072, while the sum is 38.

The square root of 21911987 is about 4681.0241400787. The cubic root of 21911987 is about 279.8297732318.

The spelling of 21911987 in words is "twenty-one million, nine hundred eleven thousand, nine hundred eighty-seven".