21513181 has 2 divisors, whose sum is σ = 21513182. Its totient is φ = 21513180.

The previous prime is 21513161. The next prime is 21513197. The reversal of 21513181 is 18131512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15729156 + 5784025 = 3966^2 + 2405^2 .

It is a cyclic number.

It is not a de Polignac number, because 21513181 - 2⁹ = 21512669 is a prime.

It is a super-2 number, since 2×21513181² = 925633913477522, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21513161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10756590 + 10756591.

It is an arithmetic number, because the mean of its divisors is an integer number (10756591).

Almost surely, 2^21513181 is an apocalyptic number.

It is an amenable number.

21513181 is a deficient number, since it is larger than the sum of its proper divisors (1).

21513181 is an equidigital number, since it uses as much as digits as its factorization.

21513181 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 21513181 is about 4638.2303737525. The cubic root of 21513181 is about 278.1217011097.

Adding to 21513181 its reverse (18131512), we get a palindrome (39644693).

The spelling of 21513181 in words is "twenty-one million, five hundred thirteen thousand, one hundred eighty-one".