21553517 has 2 divisors, whose sum is σ = 21553518. Its totient is φ = 21553516.

The previous prime is 21553487. The next prime is 21553529. The reversal of 21553517 is 71535512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14969161 + 6584356 = 3869^2 + 2566^2 .

It is a cyclic number.

It is not a de Polignac number, because 21553517 - 2⁶ = 21553453 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21553517.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21553417) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10776758 + 10776759.

It is an arithmetic number, because the mean of its divisors is an integer number (10776759).

Almost surely, 2^21553517 is an apocalyptic number.

It is an amenable number.

21553517 is a deficient number, since it is larger than the sum of its proper divisors (1).

21553517 is an equidigital number, since it uses as much as digits as its factorization.

21553517 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5250, while the sum is 29.

The square root of 21553517 is about 4642.5765475649. The cubic root of 21553517 is about 278.2954134180.

The spelling of 21553517 in words is "twenty-one million, five hundred fifty-three thousand, five hundred seventeen".