21503891 has 2 divisors, whose sum is σ = 21503892. Its totient is φ = 21503890.

The previous prime is 21503887. The next prime is 21503893. The reversal of 21503891 is 19830512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21503891 - 2² = 21503887 is a prime.

Together with 21503893, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21503893) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10751945 + 10751946.

It is an arithmetic number, because the mean of its divisors is an integer number (10751946).

Almost surely, 2^21503891 is an apocalyptic number.

21503891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21503891 is an equidigital number, since it uses as much as digits as its factorization.

21503891 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2160, while the sum is 29.

The square root of 21503891 is about 4637.2288060867. The cubic root of 21503891 is about 278.0816617403.

The spelling of 21503891 in words is "twenty-one million, five hundred three thousand, eight hundred ninety-one".