20156861 has 2 divisors, whose sum is σ = 20156862. Its totient is φ = 20156860.

The previous prime is 20156837. The next prime is 20156863. The reversal of 20156861 is 16865102.

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., 19971961 + 184900 = 4469^2 + 430^2 .

It is a cyclic number.

It is not a de Polignac number, because 20156861 - 2⁶ = 20156797 is a prime.

It is a Sophie Germain prime.

Together with 20156863, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20156863) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10078430 + 10078431.

It is an arithmetic number, because the mean of its divisors is an integer number (10078431).

Almost surely, 2^20156861 is an apocalyptic number.

It is an amenable number.

20156861 is a deficient number, since it is larger than the sum of its proper divisors (1).

20156861 is an equidigital number, since it uses as much as digits as its factorization.

20156861 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 20156861 is about 4489.6392950882. The cubic root of 20156861 is about 272.1495582137.

The spelling of 20156861 in words is "twenty million, one hundred fifty-six thousand, eight hundred sixty-one".