20663721 has 32 divisors (see below), whose sum is σ = 34917120. Its totient is φ = 11964672.

The previous prime is 20663719. The next prime is 20663737. The reversal of 20663721 is 12736602.

It is a happy number.

20663721 is a `hidden beast` number, since 2 + 0 + 6 + 637 + 21 = 666.

It is not a de Polignac number, because 20663721 - 2¹ = 20663719 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (20663761) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4236 + ... + 7698.

It is an arithmetic number, because the mean of its divisors is an integer number (1091160).

Almost surely, 2^20663721 is an apocalyptic number.

It is an amenable number.

20663721 is a deficient number, since it is larger than the sum of its proper divisors (14253399).

20663721 is a wasteful number, since it uses less digits than its factorization.

20663721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3502 (or 3496 counting only the distinct ones).

The product of its (nonzero) digits is 3024, while the sum is 27.

The square root of 20663721 is about 4545.7365739779. The cubic root of 20663721 is about 274.4118382710.

The spelling of 20663721 in words is "twenty million, six hundred sixty-three thousand, seven hundred twenty-one".