21580921 has 2 divisors, whose sum is σ = 21580922. Its totient is φ = 21580920.

The previous prime is 21580919. The next prime is 21580927. The reversal of 21580921 is 12908512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13395600 + 8185321 = 3660^2 + 2861^2 .

It is a cyclic number.

It is not a de Polignac number, because 21580921 - 2¹ = 21580919 is a prime.

Together with 21580919, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21580921.

It is not a weakly prime, because it can be changed into another prime (21580927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10790460 + 10790461.

It is an arithmetic number, because the mean of its divisors is an integer number (10790461).

Almost surely, 2^21580921 is an apocalyptic number.

It is an amenable number.

21580921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21580921 is an equidigital number, since it uses as much as digits as its factorization.

21580921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 21580921 is about 4645.5269884051. The cubic root of 21580921 is about 278.4133087576.

The spelling of 21580921 in words is "twenty-one million, five hundred eighty thousand, nine hundred twenty-one".