21599621 has 2 divisors, whose sum is σ = 21599622. Its totient is φ = 21599620.

The previous prime is 21599603. The next prime is 21599623. The reversal of 21599621 is 12699512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18395521 + 3204100 = 4289^2 + 1790^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21599621 is a prime.

It is a Sophie Germain prime.

Together with 21599623, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21599623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10799810 + 10799811.

It is an arithmetic number, because the mean of its divisors is an integer number (10799811).

Almost surely, 2^21599621 is an apocalyptic number.

It is an amenable number.

21599621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21599621 is an equidigital number, since it uses as much as digits as its factorization.

21599621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9720, while the sum is 35.

The square root of 21599621 is about 4647.5392413620. The cubic root of 21599621 is about 278.4937011534.

The spelling of 21599621 in words is "twenty-one million, five hundred ninety-nine thousand, six hundred twenty-one".