21691357 has 2 divisors, whose sum is σ = 21691358. Its totient is φ = 21691356.

The previous prime is 21691349. The next prime is 21691379. The reversal of 21691357 is 75319612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16736281 + 4955076 = 4091^2 + 2226^2 .

It is a cyclic number.

It is not a de Polignac number, because 21691357 - 2³ = 21691349 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21691457) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845678 + 10845679.

It is an arithmetic number, because the mean of its divisors is an integer number (10845679).

Almost surely, 2^21691357 is an apocalyptic number.

It is an amenable number.

21691357 is a deficient number, since it is larger than the sum of its proper divisors (1).

21691357 is an equidigital number, since it uses as much as digits as its factorization.

21691357 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11340, while the sum is 34.

The square root of 21691357 is about 4657.3980933564. The cubic root of 21691357 is about 278.8874089104.

The spelling of 21691357 in words is "twenty-one million, six hundred ninety-one thousand, three hundred fifty-seven".