21666616 has 8 divisors (see below), whose sum is σ = 40624920. Its totient is φ = 10833304.

The previous prime is 21666611. The next prime is 21666637. The reversal of 21666616 is 61666612.

It is a tau number, because it is divible by the number of its divisors (8).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1354156 + ... + 1354171.

It is an arithmetic number, because the mean of its divisors is an integer number (5078115).

Almost surely, 2^21666616 is an apocalyptic number.

It is an amenable number.

21666616 is a deficient number, since it is larger than the sum of its proper divisors (18958304).

21666616 is a wasteful number, since it uses less digits than its factorization.

21666616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2708333 (or 2708329 counting only the distinct ones).

The product of its digits is 15552, while the sum is 34.

The square root of 21666616 is about 4654.7412387801. The cubic root of 21666616 is about 278.7813362722.

The spelling of 21666616 in words is "twenty-one million, six hundred sixty-six thousand, six hundred sixteen".