21197681 has 2 divisors, whose sum is σ = 21197682. Its totient is φ = 21197680.

The previous prime is 21197677. The next prime is 21197699. The reversal of 21197681 is 18679112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17808400 + 3389281 = 4220^2 + 1841^2 .

It is a cyclic number.

It is not a de Polignac number, because 21197681 - 2² = 21197677 is a prime.

It is a super-2 number, since 2×21197681² = 898683359555522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21197621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10598840 + 10598841.

It is an arithmetic number, because the mean of its divisors is an integer number (10598841).

Almost surely, 2^21197681 is an apocalyptic number.

It is an amenable number.

21197681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21197681 is an equidigital number, since it uses as much as digits as its factorization.

21197681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6048, while the sum is 35.

The square root of 21197681 is about 4604.0939390938. The cubic root of 21197681 is about 276.7554088641.

Subtracting from 21197681 its reverse (18679112), we obtain a square (2518569 = 1587²).

The spelling of 21197681 in words is "twenty-one million, one hundred ninety-seven thousand, six hundred eighty-one".