1991212129 has 3 divisors (see below), whose sum is σ = 1991256753. Its totient is φ = 1991167506.

The previous prime is 1991212127. The next prime is 1991212163. The reversal of 1991212129 is 9212121991.

The square root of 1991212129 is 44623.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 9212121991 = 29 ⋅317659379.

It is not a de Polignac number, because 1991212129 - 2¹ = 1991212127 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991212127) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 22312 + ... + 66934.

It is an arithmetic number, because the mean of its divisors is an integer number (663752251).

Almost surely, 2^1991212129 is an apocalyptic number.

1991212129 is the 44623-rd square number.

1991212129 is the 22312-nd centered octagonal number.

It is an amenable number.

1991212129 is a deficient number, since it is larger than the sum of its proper divisors (44624).

1991212129 is an frugal number, since it uses more digits than its factorization.

1991212129 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 89246 (or 44623 counting only the distinct ones).

The product of its digits is 5832, while the sum is 37.

The cubic root of 1991212129 is about 1258.0730032374.

It can be divided in two parts, 19912 and 12129, that added together give a square (32041 = 179²).

The spelling of 1991212129 in words is "one billion, nine hundred ninety-one million, two hundred twelve thousand, one hundred twenty-nine".