21686957 has 2 divisors, whose sum is σ = 21686958. Its totient is φ = 21686956.

The previous prime is 21686947. The next prime is 21686971. The reversal of 21686957 is 75968612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11485321 + 10201636 = 3389^2 + 3194^2 .

It is a cyclic number.

It is not a de Polignac number, because 21686957 - 2¹² = 21682861 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21686927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10843478 + 10843479.

It is an arithmetic number, because the mean of its divisors is an integer number (10843479).

Almost surely, 2^21686957 is an apocalyptic number.

It is an amenable number.

21686957 is a deficient number, since it is larger than the sum of its proper divisors (1).

21686957 is an equidigital number, since it uses as much as digits as its factorization.

21686957 is an evil number, because the sum of its binary digits is even.

The product of its digits is 181440, while the sum is 44.

The square root of 21686957 is about 4656.9257026498. The cubic root of 21686957 is about 278.8685505916.

The spelling of 21686957 in words is "twenty-one million, six hundred eighty-six thousand, nine hundred fifty-seven".