28121780 has 12 divisors (see below), whose sum is σ = 59055780. Its totient is φ = 11248704.

The previous prime is 28121771. The next prime is 28121803. The reversal of 28121780 is 8712182.

It can be written as a sum of positive squares in 2 ways, for example, as 20124196 + 7997584 = 4486^2 + 2828^2 .

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 703025 + ... + 703064.

It is an arithmetic number, because the mean of its divisors is an integer number (4921315).

Almost surely, 2^28121780 is an apocalyptic number.

28121780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

28121780 is an abundant number, since it is smaller than the sum of its proper divisors (30934000).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

28121780 is a wasteful number, since it uses less digits than its factorization.

28121780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1406098 (or 1406096 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 29.

The square root of 28121780 is about 5302.9972656980. The cubic root of 28121780 is about 304.0984935933.

Adding to 28121780 its sum of digits (29), we get a square (28121809 = 5303²).

The spelling of 28121780 in words is "twenty-eight million, one hundred twenty-one thousand, seven hundred eighty".