20609721 has 20 divisors (see below), whose sum is σ = 33587664. Its totient is φ = 12490200.

The previous prime is 20609717. The next prime is 20609747. The reversal of 20609721 is 12790602.

It is not a de Polignac number, because 20609721 - 2² = 20609717 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 (20609711) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 10675 + ... + 12456.

Almost surely, 2^20609721 is an apocalyptic number.

It is an amenable number.

20609721 is a deficient number, since it is larger than the sum of its proper divisors (12977943).

20609721 is a wasteful number, since it uses less digits than its factorization.

20609721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23154 (or 23145 counting only the distinct ones).

The product of its (nonzero) digits is 1512, while the sum is 27.

The square root of 20609721 is about 4539.7930569576. The cubic root of 20609721 is about 274.1725918144.

It can be divided in two parts, 2060 and 9721, that added together give a triangular number (11781 = T₁₅₃).

The spelling of 20609721 in words is "twenty million, six hundred nine thousand, seven hundred twenty-one".