21991027 has 2 divisors, whose sum is σ = 21991028. Its totient is φ = 21991026.

The previous prime is 21991001. The next prime is 21991069. The reversal of 21991027 is 72019912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21991027 - 2¹¹ = 21988979 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21991027.

It is not a weakly prime, because it can be changed into another prime (21992027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10995513 + 10995514.

It is an arithmetic number, because the mean of its divisors is an integer number (10995514).

Almost surely, 2^21991027 is an apocalyptic number.

21991027 is a deficient number, since it is larger than the sum of its proper divisors (1).

21991027 is an equidigital number, since it uses as much as digits as its factorization.

21991027 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2268, while the sum is 31.

The square root of 21991027 is about 4689.4591372567. The cubic root of 21991027 is about 280.1658328868.

The spelling of 21991027 in words is "twenty-one million, nine hundred ninety-one thousand, twenty-seven".