21551591 has 2 divisors, whose sum is σ = 21551592. Its totient is φ = 21551590.

The previous prime is 21551587. The next prime is 21551623. The reversal of 21551591 is 19515512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21551591 - 2² = 21551587 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21551561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10775795 + 10775796.

It is an arithmetic number, because the mean of its divisors is an integer number (10775796).

Almost surely, 2^21551591 is an apocalyptic number.

21551591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21551591 is an equidigital number, since it uses as much as digits as its factorization.

21551591 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2250, while the sum is 29.

The square root of 21551591 is about 4642.3691150101. The cubic root of 21551591 is about 278.2871237743.

The spelling of 21551591 in words is "twenty-one million, five hundred fifty-one thousand, five hundred ninety-one".