21787939 has 2 divisors, whose sum is σ = 21787940. Its totient is φ = 21787938.

The previous prime is 21787907. The next prime is 21787949. The reversal of 21787939 is 93978712.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21787939 - 2⁵ = 21787907 is a prime.

It is not a weakly prime, because it can be changed into another prime (21787949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10893969 + 10893970.

It is an arithmetic number, because the mean of its divisors is an integer number (10893970).

Almost surely, 2^21787939 is an apocalyptic number.

21787939 is a deficient number, since it is larger than the sum of its proper divisors (1).

21787939 is an equidigital number, since it uses as much as digits as its factorization.

21787939 is an evil number, because the sum of its binary digits is even.

The product of its digits is 190512, while the sum is 46.

The square root of 21787939 is about 4667.7552420837. The cubic root of 21787939 is about 279.3007167706.

The spelling of 21787939 in words is "twenty-one million, seven hundred eighty-seven thousand, nine hundred thirty-nine".