20506781 has 2 divisors, whose sum is σ = 20506782. Its totient is φ = 20506780.

The previous prime is 20506771. The next prime is 20506789. The reversal of 20506781 is 18760502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19882681 + 624100 = 4459^2 + 790^2 .

It is a cyclic number.

It is not a de Polignac number, because 20506781 - 2¹⁴ = 20490397 is a prime.

It is a super-2 number, since 2×20506781² = 841056133963922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20506789) 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 as a sum of consecutive naturals, namely, 10253390 + 10253391.

It is an arithmetic number, because the mean of its divisors is an integer number (10253391).

Almost surely, 2^20506781 is an apocalyptic number.

It is an amenable number.

20506781 is a deficient number, since it is larger than the sum of its proper divisors (1).

20506781 is an equidigital number, since it uses as much as digits as its factorization.

20506781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3360, while the sum is 29.

The square root of 20506781 is about 4528.4413433322. The cubic root of 20506781 is about 273.7153569861.

The spelling of 20506781 in words is "twenty million, five hundred six thousand, seven hundred eighty-one".