28721781 has 12 divisors (see below), whose sum is σ = 45258720. Its totient is φ = 17407080.

The previous prime is 28721773. The next prime is 28721809. The reversal of 28721781 is 18712782.

It is a happy number.

It is not a de Polignac number, because 28721781 - 2³ = 28721773 is a prime.

It is a super-2 number, since 2×28721781² = 1649881407623922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28721081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 144961 + ... + 145158.

It is an arithmetic number, because the mean of its divisors is an integer number (3771560).

Almost surely, 2^28721781 is an apocalyptic number.

It is an amenable number.

28721781 is a deficient number, since it is larger than the sum of its proper divisors (16536939).

28721781 is a wasteful number, since it uses less digits than its factorization.

28721781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 290136 (or 290133 counting only the distinct ones).

The product of its digits is 12544, while the sum is 36.

The square root of 28721781 is about 5359.2705660379. The cubic root of 28721781 is about 306.2460215504.

The spelling of 28721781 in words is "twenty-eight million, seven hundred twenty-one thousand, seven hundred eighty-one".