12921781 has 4 divisors (see below), whose sum is σ = 12945952. Its totient is φ = 12897612.

The previous prime is 12921763. The next prime is 12921809. The reversal of 12921781 is 18712921.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 12921781 - 2¹¹ = 12919733 is a prime.

It is a super-2 number, since 2×12921781² = 333944848423922, which contains 22 as substring.

It is a Duffinian number.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (12921281) 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 3 ways as a sum of consecutive naturals, for example, 11265 + ... + 12358.

It is an arithmetic number, because the mean of its divisors is an integer number (3236488).

Almost surely, 2^12921781 is an apocalyptic number.

It is an amenable number.

12921781 is a deficient number, since it is larger than the sum of its proper divisors (24171).

12921781 is an equidigital number, since it uses as much as digits as its factorization.

12921781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24170.

The product of its digits is 2016, while the sum is 31.

The square root of 12921781 is about 3594.6878863122. The cubic root of 12921781 is about 234.6609324726.

The spelling of 12921781 in words is "twelve million, nine hundred twenty-one thousand, seven hundred eighty-one".