20620781 has 4 divisors (see below), whose sum is σ = 20647452. Its totient is φ = 20594112.

The previous prime is 20620777. The next prime is 20620783. The reversal of 20620781 is 18702602.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18702602 = 2 ⋅9351301.

It can be written as a sum of positive squares in 2 ways, for example, as 9954025 + 10666756 = 3155^2 + 3266^2 .

It is a cyclic number.

It is not a de Polignac number, because 20620781 - 2² = 20620777 is a prime.

It is a super-2 number, since 2×20620781² = 850433218099922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20620781.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20620783) 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, 12140 + ... + 13733.

It is an arithmetic number, because the mean of its divisors is an integer number (5161863).

Almost surely, 2^20620781 is an apocalyptic number.

It is an amenable number.

20620781 is a deficient number, since it is larger than the sum of its proper divisors (26671).

20620781 is an equidigital number, since it uses as much as digits as its factorization.

20620781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26670.

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 20620781 is about 4541.0110107772. The cubic root of 20620781 is about 274.2216270343.

The spelling of 20620781 in words is "twenty million, six hundred twenty thousand, seven hundred eighty-one".