21745661 has 12 divisors (see below), whose sum is σ = 25472160. Its totient is φ = 18509400.

The previous prime is 21745651. The next prime is 21745687. The reversal of 21745661 is 16654712.

It is a de Polignac number, because none of the positive numbers 2^k-21745661 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21745651) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5930 + ... + 8868.

It is an arithmetic number, because the mean of its divisors is an integer number (2122680).

Almost surely, 2^21745661 is an apocalyptic number.

It is an amenable number.

21745661 is a deficient number, since it is larger than the sum of its proper divisors (3726499).

21745661 is a wasteful number, since it uses less digits than its factorization.

21745661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3104 (or 3097 counting only the distinct ones).

The product of its digits is 10080, while the sum is 32.

The square root of 21745661 is about 4663.2243137126. The cubic root of 21745661 is about 279.1199451724.

The spelling of 21745661 in words is "twenty-one million, seven hundred forty-five thousand, six hundred sixty-one".