21637613 has 2 divisors, whose sum is σ = 21637614. Its totient is φ = 21637612.

The previous prime is 21637607. The next prime is 21637633. The reversal of 21637613 is 31673612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21409129 + 228484 = 4627^2 + 478^2 .

It is a cyclic number.

It is not a de Polignac number, because 21637613 - 2¹⁶ = 21572077 is a prime.

It is a Sophie Germain 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 (21637633) 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, 10818806 + 10818807.

It is an arithmetic number, because the mean of its divisors is an integer number (10818807).

Almost surely, 2^21637613 is an apocalyptic number.

It is an amenable number.

21637613 is a deficient number, since it is larger than the sum of its proper divisors (1).

21637613 is an equidigital number, since it uses as much as digits as its factorization.

21637613 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4536, while the sum is 29.

The square root of 21637613 is about 4651.6247699057. The cubic root of 21637613 is about 278.6568882036.

The spelling of 21637613 in words is "twenty-one million, six hundred thirty-seven thousand, six hundred thirteen".