21661756 has 12 divisors (see below), whose sum is σ = 37957192. Its totient is φ = 10816848.

The previous prime is 21661733. The next prime is 21661781. The reversal of 21661756 is 65716612.

It is a happy number.

It is a hoax number, since the sum of its digits (34) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 466 + ... + 6598.

Almost surely, 2^21661756 is an apocalyptic number.

It is an amenable number.

21661756 is a deficient number, since it is larger than the sum of its proper divisors (16295436).

21661756 is a wasteful number, since it uses less digits than its factorization.

21661756 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7020 (or 7018 counting only the distinct ones).

The product of its digits is 15120, while the sum is 34.

The square root of 21661756 is about 4654.2191611483. The cubic root of 21661756 is about 278.7604903986.

The spelling of 21661756 in words is "twenty-one million, six hundred sixty-one thousand, seven hundred fifty-six".