20156921 has 2 divisors, whose sum is σ = 20156922. Its totient is φ = 20156920.

The previous prime is 20156893. The next prime is 20156923. The reversal of 20156921 is 12965102.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11971600 + 8185321 = 3460^2 + 2861^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20156921 is a prime.

Together with 20156923, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20156923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10078460 + 10078461.

It is an arithmetic number, because the mean of its divisors is an integer number (10078461).

Almost surely, 2^20156921 is an apocalyptic number.

It is an amenable number.

20156921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20156921 is an equidigital number, since it uses as much as digits as its factorization.

20156921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1080, while the sum is 26.

The square root of 20156921 is about 4489.6459771345. The cubic root of 20156921 is about 272.1498282451.

The spelling of 20156921 in words is "twenty million, one hundred fifty-six thousand, nine hundred twenty-one".