21689257 has 2 divisors, whose sum is σ = 21689258. Its totient is φ = 21689256.

The previous prime is 21689237. The next prime is 21689273. The reversal of 21689257 is 75298612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18524416 + 3164841 = 4304^2 + 1779^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21689257 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21689237) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10844628 + 10844629.

It is an arithmetic number, because the mean of its divisors is an integer number (10844629).

Almost surely, 2^21689257 is an apocalyptic number.

It is an amenable number.

21689257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21689257 is an equidigital number, since it uses as much as digits as its factorization.

21689257 is an evil number, because the sum of its binary digits is even.

The product of its digits is 60480, while the sum is 40.

The square root of 21689257 is about 4657.1726401326. The cubic root of 21689257 is about 278.8784086673.

The spelling of 21689257 in words is "twenty-one million, six hundred eighty-nine thousand, two hundred fifty-seven".