20721577 has 4 divisors (see below), whose sum is σ = 20837520. Its totient is φ = 20605636.

The previous prime is 20721553. The next prime is 20721583. The reversal of 20721577 is 77512702.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20721577 - 2¹¹ = 20719529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20721377) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 57703 + ... + 58060.

It is an arithmetic number, because the mean of its divisors is an integer number (5209380).

Almost surely, 2^20721577 is an apocalyptic number.

It is an amenable number.

20721577 is a deficient number, since it is larger than the sum of its proper divisors (115943).

20721577 is a wasteful number, since it uses less digits than its factorization.

20721577 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115942.

The product of its (nonzero) digits is 6860, while the sum is 31.

The square root of 20721577 is about 4552.0958909056. The cubic root of 20721577 is about 274.6677066275.

The spelling of 20721577 in words is "twenty million, seven hundred twenty-one thousand, five hundred seventy-seven".