20656991 has 2 divisors, whose sum is σ = 20656992. Its totient is φ = 20656990.

The previous prime is 20656973. The next prime is 20657027. The reversal of 20656991 is 19965602.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20656991 - 2⁶ = 20656927 is a prime.

It is a super-2 number, since 2×20656991² = 853422554348162, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20656291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10328495 + 10328496.

It is an arithmetic number, because the mean of its divisors is an integer number (10328496).

Almost surely, 2^20656991 is an apocalyptic number.

20656991 is a deficient number, since it is larger than the sum of its proper divisors (1).

20656991 is an equidigital number, since it uses as much as digits as its factorization.

20656991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 29160, while the sum is 38.

The square root of 20656991 is about 4544.9962596244. The cubic root of 20656991 is about 274.3820438275.

The spelling of 20656991 in words is "twenty million, six hundred fifty-six thousand, nine hundred ninety-one".