21366391 has 2 divisors, whose sum is σ = 21366392. Its totient is φ = 21366390.

The previous prime is 21366377. The next prime is 21366403. The reversal of 21366391 is 19366312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21366391 - 2¹³ = 21358199 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21366311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10683195 + 10683196.

It is an arithmetic number, because the mean of its divisors is an integer number (10683196).

Almost surely, 2^21366391 is an apocalyptic number.

21366391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21366391 is an equidigital number, since it uses as much as digits as its factorization.

21366391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5832, while the sum is 31.

The square root of 21366391 is about 4622.3793656514. The cubic root of 21366391 is about 277.4876914704.

The spelling of 21366391 in words is "twenty-one million, three hundred sixty-six thousand, three hundred ninety-one".