20661691 has 2 divisors, whose sum is σ = 20661692. Its totient is φ = 20661690.

The previous prime is 20661689. The next prime is 20661703. The reversal of 20661691 is 19616602.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20661691 - 2¹ = 20661689 is a prime.

Together with 20661689, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (20661631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10330845 + 10330846.

It is an arithmetic number, because the mean of its divisors is an integer number (10330846).

Almost surely, 2^20661691 is an apocalyptic number.

20661691 is a deficient number, since it is larger than the sum of its proper divisors (1).

20661691 is an equidigital number, since it uses as much as digits as its factorization.

20661691 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3888, while the sum is 31.

The square root of 20661691 is about 4545.5132823478. The cubic root of 20661691 is about 274.4028519212.

The spelling of 20661691 in words is "twenty million, six hundred sixty-one thousand, six hundred ninety-one".