28781381 has 4 divisors (see below), whose sum is σ = 28872492. Its totient is φ = 28690272.

The previous prime is 28781317. The next prime is 28781387. The reversal of 28781381 is 18318782.

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

It can be written as a sum of positive squares in 2 ways, for example, as 1050625 + 27730756 = 1025^2 + 5266^2 .

It is a cyclic number.

It is not a de Polignac number, because 28781381 - 2⁶ = 28781317 is a prime.

It is a super-2 number, since 2×28781381² = 1656735784534322, 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 (28781387) 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, 45080 + ... + 45713.

It is an arithmetic number, because the mean of its divisors is an integer number (7218123).

Almost surely, 2^28781381 is an apocalyptic number.

It is an amenable number.

28781381 is a deficient number, since it is larger than the sum of its proper divisors (91111).

28781381 is an equidigital number, since it uses as much as digits as its factorization.

28781381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91110.

The product of its digits is 21504, while the sum is 38.

The square root of 28781381 is about 5364.8281426342. The cubic root of 28781381 is about 306.4577035540.

The spelling of 28781381 in words is "twenty-eight million, seven hundred eighty-one thousand, three hundred eighty-one".