21397787 has 2 divisors, whose sum is σ = 21397788. Its totient is φ = 21397786.

The previous prime is 21397771. The next prime is 21397807. The reversal of 21397787 is 78779312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21397787 - 2⁴ = 21397771 is a prime.

It is not a weakly prime, because it can be changed into another prime (21397487) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10698893 + 10698894.

It is an arithmetic number, because the mean of its divisors is an integer number (10698894).

Almost surely, 2^21397787 is an apocalyptic number.

21397787 is a deficient number, since it is larger than the sum of its proper divisors (1).

21397787 is an equidigital number, since it uses as much as digits as its factorization.

21397787 is an evil number, because the sum of its binary digits is even.

The product of its digits is 148176, while the sum is 44.

The square root of 21397787 is about 4625.7742054709. The cubic root of 21397787 is about 277.6235393989.

The spelling of 21397787 in words is "twenty-one million, three hundred ninety-seven thousand, seven hundred eighty-seven".