21553717 has 2 divisors, whose sum is σ = 21553718. Its totient is φ = 21553716.

The previous prime is 21553643. The next prime is 21553787. The reversal of 21553717 is 71735512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17589636 + 3964081 = 4194^2 + 1991^2 .

It is a cyclic number.

It is not a de Polignac number, because 21553717 - 2¹⁵ = 21520949 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21553787) 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, 10776858 + 10776859.

It is an arithmetic number, because the mean of its divisors is an integer number (10776859).

Almost surely, 2^21553717 is an apocalyptic number.

It is an amenable number.

21553717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21553717 is an equidigital number, since it uses as much as digits as its factorization.

21553717 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7350, while the sum is 31.

The square root of 21553717 is about 4642.5980872783. The cubic root of 21553717 is about 278.2962742043.

The spelling of 21553717 in words is "twenty-one million, five hundred fifty-three thousand, seven hundred seventeen".