21129999991 has 2 divisors, whose sum is σ = 21129999992. Its totient is φ = 21129999990.

The previous prime is 21129999971. The next prime is 21130000033. The reversal of 21129999991 is 19999992112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21129999991 - 2¹⁵ = 21129967223 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21129999971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10564999995 + 10564999996.

It is an arithmetic number, because the mean of its divisors is an integer number (10564999996).

Almost surely, 2^21129999991 is an apocalyptic number.

21129999991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21129999991 is an equidigital number, since it uses as much as digits as its factorization.

21129999991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2125764, while the sum is 61.

The spelling of 21129999991 in words is "twenty-one billion, one hundred twenty-nine million, nine hundred ninety-nine thousand, nine hundred ninety-one".