21553613 has 2 divisors, whose sum is σ = 21553614. Its totient is φ = 21553612.

The previous prime is 21553531. The next prime is 21553627. The reversal of 21553613 is 31635512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19695844 + 1857769 = 4438^2 + 1363^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21553613 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 (21553633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10776806 + 10776807.

It is an arithmetic number, because the mean of its divisors is an integer number (10776807).

Almost surely, 2^21553613 is an apocalyptic number.

It is an amenable number.

21553613 is a deficient number, since it is larger than the sum of its proper divisors (1).

21553613 is an equidigital number, since it uses as much as digits as its factorization.

21553613 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2700, while the sum is 26.

The square root of 21553613 is about 4642.5868866398. The cubic root of 21553613 is about 278.2958265961.

The spelling of 21553613 in words is "twenty-one million, five hundred fifty-three thousand, six hundred thirteen".