20671781 has 4 divisors (see below), whose sum is σ = 22261932. Its totient is φ = 19081632.

The previous prime is 20671769. The next prime is 20671811. The reversal of 20671781 is 18717602.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18717602 = 2 ⋅9358801.

It can be written as a sum of positive squares in 2 ways, for example, as 14250625 + 6421156 = 3775^2 + 2534^2 .

It is a cyclic number.

It is not a de Polignac number, because 20671781 - 2¹⁰ = 20670757 is a prime.

It is a super-2 number, since 2×20671781² = 854645059423922, 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 (20671081) 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, 795056 + ... + 795081.

It is an arithmetic number, because the mean of its divisors is an integer number (5565483).

Almost surely, 2^20671781 is an apocalyptic number.

It is an amenable number.

20671781 is a deficient number, since it is larger than the sum of its proper divisors (1590151).

20671781 is a wasteful number, since it uses less digits than its factorization.

20671781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1590150.

The product of its (nonzero) digits is 4704, while the sum is 32.

The square root of 20671781 is about 4546.6230325374. The cubic root of 20671781 is about 274.4475122575.

The spelling of 20671781 in words is "twenty million, six hundred seventy-one thousand, seven hundred eighty-one".