21535621 has 2 divisors, whose sum is σ = 21535622. Its totient is φ = 21535620.

The previous prime is 21535601. The next prime is 21535639. The reversal of 21535621 is 12653512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14976900 + 6558721 = 3870^2 + 2561^2 .

It is a cyclic number.

It is not a de Polignac number, because 21535621 - 2⁵ = 21535589 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21535601) 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, 10767810 + 10767811.

It is an arithmetic number, because the mean of its divisors is an integer number (10767811).

Almost surely, 2^21535621 is an apocalyptic number.

It is an amenable number.

21535621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21535621 is an equidigital number, since it uses as much as digits as its factorization.

21535621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1800, while the sum is 25.

The square root of 21535621 is about 4640.6487692994. The cubic root of 21535621 is about 278.2183687024.

The spelling of 21535621 in words is "twenty-one million, five hundred thirty-five thousand, six hundred twenty-one".