21065621 has 2 divisors, whose sum is σ = 21065622. Its totient is φ = 21065620.

The previous prime is 21065609. The next prime is 21065641. The reversal of 21065621 is 12656012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21031396 + 34225 = 4586^2 + 185^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21065621 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21065641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10532810 + 10532811.

It is an arithmetic number, because the mean of its divisors is an integer number (10532811).

Almost surely, 2^21065621 is an apocalyptic number.

It is an amenable number.

21065621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21065621 is an equidigital number, since it uses as much as digits as its factorization.

21065621 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21065621 is about 4589.7299484828. The cubic root of 21065621 is about 276.1794892488.

The spelling of 21065621 in words is "twenty-one million, sixty-five thousand, six hundred twenty-one".