20728751 has 4 divisors (see below), whose sum is σ = 20741904. Its totient is φ = 20715600.

The previous prime is 20728733. The next prime is 20728759. The reversal of 20728751 is 15782702.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20728751 is a prime.

It is a super-2 number, since 2×20728751² = 859362236040002, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20728759) 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, 3830 + ... + 7491.

It is an arithmetic number, because the mean of its divisors is an integer number (5185476).

Almost surely, 2^20728751 is an apocalyptic number.

20728751 is a deficient number, since it is larger than the sum of its proper divisors (13153).

20728751 is a wasteful number, since it uses less digits than its factorization.

20728751 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13152.

The product of its (nonzero) digits is 7840, while the sum is 32.

The square root of 20728751 is about 4552.8838113881. The cubic root of 20728751 is about 274.6994004632.

The spelling of 20728751 in words is "twenty million, seven hundred twenty-eight thousand, seven hundred fifty-one".