21388891 has 2 divisors, whose sum is σ = 21388892. Its totient is φ = 21388890.

The previous prime is 21388883. The next prime is 21388897. The reversal of 21388891 is 19888312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21388891 - 2³ = 21388883 is a prime.

It is not a weakly prime, because it can be changed into another prime (21388897) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10694445 + 10694446.

It is an arithmetic number, because the mean of its divisors is an integer number (10694446).

Almost surely, 2^21388891 is an apocalyptic number.

21388891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21388891 is an equidigital number, since it uses as much as digits as its factorization.

21388891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 27648, while the sum is 40.

The square root of 21388891 is about 4624.8125367414. The cubic root of 21388891 is about 277.5850606325.

The spelling of 21388891 in words is "twenty-one million, three hundred eighty-eight thousand, eight hundred ninety-one".