21648551 has 2 divisors, whose sum is σ = 21648552. Its totient is φ = 21648550.

The previous prime is 21648541. The next prime is 21648553. The reversal of 21648551 is 15584612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21648551 - 2²² = 17454247 is a prime.

Together with 21648553, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21648553) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10824275 + 10824276.

It is an arithmetic number, because the mean of its divisors is an integer number (10824276).

Almost surely, 2^21648551 is an apocalyptic number.

21648551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21648551 is an equidigital number, since it uses as much as digits as its factorization.

21648551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9600, while the sum is 32.

The square root of 21648551 is about 4652.8003395805. The cubic root of 21648551 is about 278.7038347807.

The spelling of 21648551 in words is "twenty-one million, six hundred forty-eight thousand, five hundred fifty-one".