21620591 has 2 divisors, whose sum is σ = 21620592. Its totient is φ = 21620590.

The previous prime is 21620581. The next prime is 21620593. The reversal of 21620591 is 19502612.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21620591 is a prime.

Together with 21620593, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21620591.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21620593) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810295 + 10810296.

It is an arithmetic number, because the mean of its divisors is an integer number (10810296).

Almost surely, 2^21620591 is an apocalyptic number.

21620591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21620591 is an equidigital number, since it uses as much as digits as its factorization.

21620591 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1080, while the sum is 26.

The square root of 21620591 is about 4649.7947266519. The cubic root of 21620591 is about 278.5837972405.

The spelling of 21620591 in words is "twenty-one million, six hundred twenty thousand, five hundred ninety-one".