21611591 has 2 divisors, whose sum is σ = 21611592. Its totient is φ = 21611590.

The previous prime is 21611567. The next prime is 21611609. The reversal of 21611591 is 19511612.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21611591 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 21611591.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21611791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10805795 + 10805796.

It is an arithmetic number, because the mean of its divisors is an integer number (10805796).

Almost surely, 2^21611591 is an apocalyptic number.

21611591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21611591 is an equidigital number, since it uses as much as digits as its factorization.

21611591 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 540, while the sum is 26.

The square root of 21611591 is about 4648.8268412579. The cubic root of 21611591 is about 278.5451365311.

The spelling of 21611591 in words is "twenty-one million, six hundred eleven thousand, five hundred ninety-one".