21905617 has 2 divisors, whose sum is σ = 21905618. Its totient is φ = 21905616.

The previous prime is 21905593. The next prime is 21905627. The reversal of 21905617 is 71650912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15062161 + 6843456 = 3881^2 + 2616^2 .

It is a cyclic number.

It is not a de Polignac number, because 21905617 - 2⁷ = 21905489 is a prime.

It is not a weakly prime, because it can be changed into another prime (21905627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10952808 + 10952809.

It is an arithmetic number, because the mean of its divisors is an integer number (10952809).

Almost surely, 2^21905617 is an apocalyptic number.

It is an amenable number.

21905617 is a deficient number, since it is larger than the sum of its proper divisors (1).

21905617 is an equidigital number, since it uses as much as digits as its factorization.

21905617 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3780, while the sum is 31.

The square root of 21905617 is about 4680.3436839617. The cubic root of 21905617 is about 279.8026543096.

It can be divided in two parts, 21905 and 617, that added together give a palindrome (22522).

The spelling of 21905617 in words is "twenty-one million, nine hundred five thousand, six hundred seventeen".