21578681 has 2 divisors, whose sum is σ = 21578682. Its totient is φ = 21578680.

The previous prime is 21578671. The next prime is 21578731. The reversal of 21578681 is 18687512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16362025 + 5216656 = 4045^2 + 2284^2 .

It is a cyclic number.

It is not a de Polignac number, because 21578681 - 2⁶ = 21578617 is a prime.

It is a super-2 number, since 2×21578681² = 931278947399522, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21578651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10789340 + 10789341.

It is an arithmetic number, because the mean of its divisors is an integer number (10789341).

Almost surely, 2^21578681 is an apocalyptic number.

It is an amenable number.

21578681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21578681 is an equidigital number, since it uses as much as digits as its factorization.

21578681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 26880, while the sum is 38.

The square root of 21578681 is about 4645.2858900180. The cubic root of 21578681 is about 278.4036757522.

The spelling of 21578681 in words is "twenty-one million, five hundred seventy-eight thousand, six hundred eighty-one".