20942781 has 4 divisors (see below), whose sum is σ = 27923712. Its totient is φ = 13961852.

The previous prime is 20942771. The next prime is 20942783. The reversal of 20942781 is 18724902.

It is a happy number.

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 20942781 - 2⁵ = 20942749 is a prime.

It is a super-2 number, since 2×20942781² = 877200152027922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20942783) 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, 3490461 + ... + 3490466.

It is an arithmetic number, because the mean of its divisors is an integer number (6980928).

Almost surely, 2^20942781 is an apocalyptic number.

It is an amenable number.

20942781 is a deficient number, since it is larger than the sum of its proper divisors (6980931).

20942781 is an equidigital number, since it uses as much as digits as its factorization.

20942781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6980930.

The product of its (nonzero) digits is 8064, while the sum is 33.

The square root of 20942781 is about 4576.3283317524. The cubic root of 20942781 is about 275.6416137064.

The spelling of 20942781 in words is "twenty million, nine hundred forty-two thousand, seven hundred eighty-one".