18991261 has 8 divisors (see below), whose sum is σ = 20983104. Its totient is φ = 17096640.

The previous prime is 18991253. The next prime is 18991267. The reversal of 18991261 is 16219981.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 18991261 - 2³ = 18991253 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18991261.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18991267) 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 in 7 ways as a sum of consecutive naturals, for example, 23895 + ... + 24676.

It is an arithmetic number, because the mean of its divisors is an integer number (2622888).

Almost surely, 2^18991261 is an apocalyptic number.

It is an amenable number.

18991261 is a deficient number, since it is larger than the sum of its proper divisors (1991843).

18991261 is a wasteful number, since it uses less digits than its factorization.

18991261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 48611.

The product of its digits is 7776, while the sum is 37.

The square root of 18991261 is about 4357.8963961985. The cubic root of 18991261 is about 266.7992477878.

It can be divided in two parts, 1899 and 1261, that added together give a triangular number (3160 = T₇₉).

The spelling of 18991261 in words is "eighteen million, nine hundred ninety-one thousand, two hundred sixty-one".