20406781 has 2 divisors, whose sum is σ = 20406782. Its totient is φ = 20406780.

The previous prime is 20406767. The next prime is 20406791. The reversal of 20406781 is 18760402.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18844281 + 1562500 = 4341^2 + 1250^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20406781 is a prime.

It is a super-2 number, since 2×20406781² = 832873421563922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20406791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10203390 + 10203391.

It is an arithmetic number, because the mean of its divisors is an integer number (10203391).

Almost surely, 2^20406781 is an apocalyptic number.

It is an amenable number.

20406781 is a deficient number, since it is larger than the sum of its proper divisors (1).

20406781 is an equidigital number, since it uses as much as digits as its factorization.

20406781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2688, while the sum is 28.

The square root of 20406781 is about 4517.3865232012. The cubic root of 20406781 is about 273.2697133643.

The spelling of 20406781 in words is "twenty million, four hundred six thousand, seven hundred eighty-one".