20730781 has 2 divisors, whose sum is σ = 20730782. Its totient is φ = 20730780.

The previous prime is 20730757. The next prime is 20730799. The reversal of 20730781 is 18703702.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10458756 + 10272025 = 3234^2 + 3205^2 .

It is a cyclic number.

It is not a de Polignac number, because 20730781 - 2¹¹ = 20728733 is a prime.

It is a super-2 number, since 2×20730781² = 859530561739922, 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 (20730481) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10365390 + 10365391.

It is an arithmetic number, because the mean of its divisors is an integer number (10365391).

Almost surely, 2^20730781 is an apocalyptic number.

It is an amenable number.

20730781 is a deficient number, since it is larger than the sum of its proper divisors (1).

20730781 is an equidigital number, since it uses as much as digits as its factorization.

20730781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2352, while the sum is 28.

The square root of 20730781 is about 4553.1067415557. The cubic root of 20730781 is about 274.7083674222.

The spelling of 20730781 in words is "twenty million, seven hundred thirty thousand, seven hundred eighty-one".