21647617 has 2 divisors, whose sum is σ = 21647618. Its totient is φ = 21647616.

The previous prime is 21647609. The next prime is 21647621. The reversal of 21647617 is 71674612.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17631601 + 4016016 = 4199^2 + 2004^2 .

It is a cyclic number.

It is not a de Polignac number, because 21647617 - 2³ = 21647609 is a prime.

It is not a weakly prime, because it can be changed into another prime (21647657) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10823808 + 10823809.

It is an arithmetic number, because the mean of its divisors is an integer number (10823809).

Almost surely, 2^21647617 is an apocalyptic number.

It is an amenable number.

21647617 is a deficient number, since it is larger than the sum of its proper divisors (1).

21647617 is an equidigital number, since it uses as much as digits as its factorization.

21647617 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14112, while the sum is 34.

The square root of 21647617 is about 4652.6999688353. The cubic root of 21647617 is about 278.6998266121.

The spelling of 21647617 in words is "twenty-one million, six hundred forty-seven thousand, six hundred seventeen".