28187781 has 16 divisors (see below), whose sum is σ = 38776320. Its totient is φ = 18205040.

The previous prime is 28187767. The next prime is 28187791. The reversal of 28187781 is 18778182.

It is not a de Polignac number, because 28187781 - 2⁵ = 28187749 is a prime.

It is a super-2 number, since 2×28187781² = 1589101995407922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28187791) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11446 + ... + 13688.

It is an arithmetic number, because the mean of its divisors is an integer number (2423520).

Almost surely, 2^28187781 is an apocalyptic number.

It is an amenable number.

28187781 is a deficient number, since it is larger than the sum of its proper divisors (10588539).

28187781 is a wasteful number, since it uses less digits than its factorization.

28187781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2376.

The product of its digits is 50176, while the sum is 42.

The square root of 28187781 is about 5309.2166088793. The cubic root of 28187781 is about 304.3362111589.

The spelling of 28187781 in words is "twenty-eight million, one hundred eighty-seven thousand, seven hundred eighty-one".