21551791 has 2 divisors, whose sum is σ = 21551792. Its totient is φ = 21551790.

The previous prime is 21551743. The next prime is 21551819. The reversal of 21551791 is 19715512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21551791 - 2¹⁷ = 21420719 is a prime.

It is a zygodrome in base 3.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21551701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10775895 + 10775896.

It is an arithmetic number, because the mean of its divisors is an integer number (10775896).

Almost surely, 2^21551791 is an apocalyptic number.

21551791 is a deficient number, since it is larger than the sum of its proper divisors (1).

21551791 is an equidigital number, since it uses as much as digits as its factorization.

21551791 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3150, while the sum is 31.

The square root of 21551791 is about 4642.3906556859. The cubic root of 21551791 is about 278.2879846118.

The spelling of 21551791 in words is "twenty-one million, five hundred fifty-one thousand, seven hundred ninety-one".