21898391 has 2 divisors, whose sum is σ = 21898392. Its totient is φ = 21898390.

The previous prime is 21898379. The next prime is 21898399. The reversal of 21898391 is 19389812.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21898391 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21898399) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10949195 + 10949196.

It is an arithmetic number, because the mean of its divisors is an integer number (10949196).

Almost surely, 2^21898391 is an apocalyptic number.

21898391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21898391 is an equidigital number, since it uses as much as digits as its factorization.

21898391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 31104, while the sum is 41.

The square root of 21898391 is about 4679.5716684329. The cubic root of 21898391 is about 279.7718847839.

The spelling of 21898391 in words is "twenty-one million, eight hundred ninety-eight thousand, three hundred ninety-one".