21552551 has 2 divisors, whose sum is σ = 21552552. Its totient is φ = 21552550.

The previous prime is 21552529. The next prime is 21552563. The reversal of 21552551 is 15525512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21552551 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 21552551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21552521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10776275 + 10776276.

It is an arithmetic number, because the mean of its divisors is an integer number (10776276).

Almost surely, 2^21552551 is an apocalyptic number.

21552551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21552551 is an equidigital number, since it uses as much as digits as its factorization.

21552551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2500, while the sum is 26.

The square root of 21552551 is about 4642.4725093424. The cubic root of 21552551 is about 278.2912557457.

The spelling of 21552551 in words is "twenty-one million, five hundred fifty-two thousand, five hundred fifty-one".