21697657 has 2 divisors, whose sum is σ = 21697658. Its totient is φ = 21697656.

The previous prime is 21697633. The next prime is 21697667. The reversal of 21697657 is 75679612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21678336 + 19321 = 4656^2 + 139^2 .

It is a cyclic number.

It is not a de Polignac number, because 21697657 - 2¹⁵ = 21664889 is a prime.

It is not a weakly prime, because it can be changed into another prime (21697667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10848828 + 10848829.

It is an arithmetic number, because the mean of its divisors is an integer number (10848829).

Almost surely, 2^21697657 is an apocalyptic number.

It is an amenable number.

21697657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21697657 is an equidigital number, since it uses as much as digits as its factorization.

21697657 is an evil number, because the sum of its binary digits is even.

The product of its digits is 158760, while the sum is 43.

The square root of 21697657 is about 4658.0743875554. The cubic root of 21697657 is about 278.9144061549.

The spelling of 21697657 in words is "twenty-one million, six hundred ninety-seven thousand, six hundred fifty-seven".