21920989 has 2 divisors, whose sum is σ = 21920990. Its totient is φ = 21920988.

The previous prime is 21920963. The next prime is 21921017. The reversal of 21920989 is 98902912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17264025 + 4656964 = 4155^2 + 2158^2 .

It is a cyclic number.

It is not a de Polignac number, because 21920989 - 2¹⁷ = 21789917 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21920929) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10960494 + 10960495.

It is an arithmetic number, because the mean of its divisors is an integer number (10960495).

Almost surely, 2^21920989 is an apocalyptic number.

It is an amenable number.

21920989 is a deficient number, since it is larger than the sum of its proper divisors (1).

21920989 is an equidigital number, since it uses as much as digits as its factorization.

21920989 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 23328, while the sum is 40.

The square root of 21920989 is about 4681.9855830620. The cubic root of 21920989 is about 279.8680883747.

The spelling of 21920989 in words is "twenty-one million, nine hundred twenty thousand, nine hundred eighty-nine".