21971387 has 2 divisors, whose sum is σ = 21971388. Its totient is φ = 21971386.

The previous prime is 21971359. The next prime is 21971393. The reversal of 21971387 is 78317912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21971387 - 2¹⁰ = 21970363 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21971387.

It is not a weakly prime, because it can be changed into another prime (21971687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10985693 + 10985694.

It is an arithmetic number, because the mean of its divisors is an integer number (10985694).

Almost surely, 2^21971387 is an apocalyptic number.

21971387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21971387 is an equidigital number, since it uses as much as digits as its factorization.

21971387 is an evil number, because the sum of its binary digits is even.

The product of its digits is 21168, while the sum is 38.

The square root of 21971387 is about 4687.3646113781. The cubic root of 21971387 is about 280.0824034675.

The spelling of 21971387 in words is "twenty-one million, nine hundred seventy-one thousand, three hundred eighty-seven".