21152581 has 2 divisors, whose sum is σ = 21152582. Its totient is φ = 21152580.

The previous prime is 21152569. The next prime is 21152587. The reversal of 21152581 is 18525112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14130081 + 7022500 = 3759^2 + 2650^2 .

It is a cyclic number.

It is not a de Polignac number, because 21152581 - 2⁹ = 21152069 is a prime.

It is a super-2 number, since 2×21152581² = 894863365923122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21152587) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10576290 + 10576291.

It is an arithmetic number, because the mean of its divisors is an integer number (10576291).

Almost surely, 2^21152581 is an apocalyptic number.

It is an amenable number.

21152581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21152581 is an equidigital number, since it uses as much as digits as its factorization.

21152581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 800, while the sum is 25.

The square root of 21152581 is about 4599.1935162591. The cubic root of 21152581 is about 276.5589953762.

Adding to 21152581 its reverse (18525112), we get a palindrome (39677693).

The spelling of 21152581 in words is "twenty-one million, one hundred fifty-two thousand, five hundred eighty-one".