21113581 has 2 divisors, whose sum is σ = 21113582. Its totient is φ = 21113580.

The previous prime is 21113549. The next prime is 21113591. The reversal of 21113581 is 18531112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20848356 + 265225 = 4566^2 + 515^2 .

It is a cyclic number.

It is not a de Polignac number, because 21113581 - 2⁵ = 21113549 is a prime.

It is a super-2 number, since 2×21113581² = 891566605287122, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21113591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10556790 + 10556791.

It is an arithmetic number, because the mean of its divisors is an integer number (10556791).

Almost surely, 2^21113581 is an apocalyptic number.

It is an amenable number.

21113581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21113581 is an equidigital number, since it uses as much as digits as its factorization.

21113581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 240, while the sum is 22.

The square root of 21113581 is about 4594.9516863619. The cubic root of 21113581 is about 276.3889225708.

Adding to 21113581 its reverse (18531112), we get a palindrome (39644693).

The spelling of 21113581 in words is "twenty-one million, one hundred thirteen thousand, five hundred eighty-one".