21681797 has 2 divisors, whose sum is σ = 21681798. Its totient is φ = 21681796.

The previous prime is 21681769. The next prime is 21681799. The reversal of 21681797 is 79718612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10962721 + 10719076 = 3311^2 + 3274^2 .

It is a cyclic number.

It is not a de Polignac number, because 21681797 - 2¹² = 21677701 is a prime.

It is a super-2 number, since 2×21681797² = 940200642298418, which contains 22 as substring.

Together with 21681799, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21681799) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10840898 + 10840899.

It is an arithmetic number, because the mean of its divisors is an integer number (10840899).

Almost surely, 2^21681797 is an apocalyptic number.

It is an amenable number.

21681797 is a deficient number, since it is larger than the sum of its proper divisors (1).

21681797 is an equidigital number, since it uses as much as digits as its factorization.

21681797 is an evil number, because the sum of its binary digits is even.

The product of its digits is 42336, while the sum is 41.

The square root of 21681797 is about 4656.3716561288. The cubic root of 21681797 is about 278.8464316768.

The spelling of 21681797 in words is "twenty-one million, six hundred eighty-one thousand, seven hundred ninety-seven".