20781251 has 2 divisors, whose sum is σ = 20781252. Its totient is φ = 20781250.

The previous prime is 20781239. The next prime is 20781263. The reversal of 20781251 is 15218702.

It is a balanced prime because it is at equal distance from previous prime (20781239) and next prime (20781263).

It is a cyclic number.

It is not a de Polignac number, because 20781251 - 2¹⁴ = 20764867 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20781251.

It is not a weakly prime, because it can be changed into another prime (20781221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10390625 + 10390626.

It is an arithmetic number, because the mean of its divisors is an integer number (10390626).

Almost surely, 2^20781251 is an apocalyptic number.

20781251 is a deficient number, since it is larger than the sum of its proper divisors (1).

20781251 is an equidigital number, since it uses as much as digits as its factorization.

20781251 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 20781251 is about 4558.6457418843. The cubic root of 20781251 is about 274.9311166315.

Adding to 20781251 its reverse (15218702), we get a palindrome (35999953).

The spelling of 20781251 in words is "twenty million, seven hundred eighty-one thousand, two hundred fifty-one".