21387851 has 2 divisors, whose sum is σ = 21387852. Its totient is φ = 21387850.

The previous prime is 21387841. The next prime is 21387893. The reversal of 21387851 is 15878312.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21387851 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21387811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10693925 + 10693926.

It is an arithmetic number, because the mean of its divisors is an integer number (10693926).

Almost surely, 2^21387851 is an apocalyptic number.

21387851 is a deficient number, since it is larger than the sum of its proper divisors (1).

21387851 is an equidigital number, since it uses as much as digits as its factorization.

21387851 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13440, while the sum is 35.

The square root of 21387851 is about 4624.7000983848. The cubic root of 21387851 is about 277.5805615190.

The spelling of 21387851 in words is "twenty-one million, three hundred eighty-seven thousand, eight hundred fifty-one".