20997971 has 2 divisors, whose sum is σ = 20997972. Its totient is φ = 20997970.

The previous prime is 20997961. The next prime is 20997973. The reversal of 20997971 is 17979902.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20997971 is a prime.

It is a super-2 number, since 2×20997971² = 881829572233682, which contains 22 as substring.

Together with 20997973, 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 (20997973) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10498985 + 10498986.

It is an arithmetic number, because the mean of its divisors is an integer number (10498986).

Almost surely, 2^20997971 is an apocalyptic number.

20997971 is a deficient number, since it is larger than the sum of its proper divisors (1).

20997971 is an equidigital number, since it uses as much as digits as its factorization.

20997971 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 71442, while the sum is 44.

The square root of 20997971 is about 4582.3543075585. The cubic root of 20997971 is about 275.8835318644.

The spelling of 20997971 in words is "twenty million, nine hundred ninety-seven thousand, nine hundred seventy-one".