20731681 has 2 divisors, whose sum is σ = 20731682. Its totient is φ = 20731680.

The previous prime is 20731663. The next prime is 20731699. The reversal of 20731681 is 18613702.

It is a balanced prime because it is at equal distance from previous prime (20731663) and next prime (20731699).

It can be written as a sum of positive squares in only one way, i.e., 19713600 + 1018081 = 4440^2 + 1009^2 .

It is a cyclic number.

It is not a de Polignac number, because 20731681 - 2⁷ = 20731553 is a prime.

It is a super-2 number, since 2×20731681² = 859605194171522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20731651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10365840 + 10365841.

It is an arithmetic number, because the mean of its divisors is an integer number (10365841).

Almost surely, 2^20731681 is an apocalyptic number.

It is an amenable number.

20731681 is a deficient number, since it is larger than the sum of its proper divisors (1).

20731681 is an equidigital number, since it uses as much as digits as its factorization.

20731681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 20731681 is about 4553.2055740983. The cubic root of 20731681 is about 274.7123427340.

It can be divided in two parts, 20731 and 681, that added together give a palindrome (21412).

The spelling of 20731681 in words is "twenty million, seven hundred thirty-one thousand, six hundred eighty-one".