21440681 has 2 divisors, whose sum is σ = 21440682. Its totient is φ = 21440680.

The previous prime is 21440677. The next prime is 21440687. The reversal of 21440681 is 18604412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21307456 + 133225 = 4616^2 + 365^2 .

It is a cyclic number.

It is not a de Polignac number, because 21440681 - 2² = 21440677 is a prime.

It is a super-2 number, since 2×21440681² = 919405603487522, which contains 22 as substring.

It is a plaindrome in base 11.

It is a self number, because there is not a number n which added to its sum of digits gives 21440681.

It is not a weakly prime, because it can be changed into another prime (21440687) 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, 10720340 + 10720341.

It is an arithmetic number, because the mean of its divisors is an integer number (10720341).

Almost surely, 2^21440681 is an apocalyptic number.

It is an amenable number.

21440681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21440681 is an equidigital number, since it uses as much as digits as its factorization.

21440681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1536, while the sum is 26.

The square root of 21440681 is about 4630.4082973319. The cubic root of 21440681 is about 277.8089236128.

The spelling of 21440681 in words is "twenty-one million, four hundred forty thousand, six hundred eighty-one".