21051691 has 2 divisors, whose sum is σ = 21051692. Its totient is φ = 21051690.

The previous prime is 21051673. The next prime is 21051703. The reversal of 21051691 is 19615012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21051691 - 2¹¹ = 21049643 is a prime.

It is not a weakly prime, because it can be changed into another prime (21051091) 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, 10525845 + 10525846.

It is an arithmetic number, because the mean of its divisors is an integer number (10525846).

Almost surely, 2^21051691 is an apocalyptic number.

21051691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21051691 is an equidigital number, since it uses as much as digits as its factorization.

21051691 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 540, while the sum is 25.

The square root of 21051691 is about 4588.2121790519. The cubic root of 21051691 is about 276.1185996980.

The spelling of 21051691 in words is "twenty-one million, fifty-one thousand, six hundred ninety-one".