21647657 has 2 divisors, whose sum is σ = 21647658. Its totient is φ = 21647656.

The previous prime is 21647653. The next prime is 21647693. The reversal of 21647657 is 75674612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17106496 + 4541161 = 4136^2 + 2131^2 .

It is a cyclic number.

It is not a de Polignac number, because 21647657 - 2² = 21647653 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21647657.

It is not a weakly prime, because it can be changed into another prime (21647653) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10823828 + 10823829.

It is an arithmetic number, because the mean of its divisors is an integer number (10823829).

Almost surely, 2^21647657 is an apocalyptic number.

It is an amenable number.

21647657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21647657 is an equidigital number, since it uses as much as digits as its factorization.

21647657 is an evil number, because the sum of its binary digits is even.

The product of its digits is 70560, while the sum is 38.

The square root of 21647657 is about 4652.7042674127. The cubic root of 21647657 is about 278.6999982705.

The spelling of 21647657 in words is "twenty-one million, six hundred forty-seven thousand, six hundred fifty-seven".