19991917 has 4 divisors (see below), whose sum is σ = 21809376. Its totient is φ = 18174460.

The previous prime is 19991911. The next prime is 19991963. The reversal of 19991917 is 71919991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 19991917 - 2⁷ = 19991789 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19991911) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 908713 + ... + 908734.

It is an arithmetic number, because the mean of its divisors is an integer number (5452344).

Almost surely, 2^19991917 is an apocalyptic number.

It is an amenable number.

19991917 is a deficient number, since it is larger than the sum of its proper divisors (1817459).

19991917 is a wasteful number, since it uses less digits than its factorization.

19991917 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1817458.

The product of its digits is 45927, while the sum is 46.

The square root of 19991917 is about 4471.2321567997. The cubic root of 19991917 is about 271.4051890028.

It can be divided in two parts, 1999 and 1917, that added together give a triangular number (3916 = T₈₈).

The spelling of 19991917 in words is "nineteen million, nine hundred ninety-one thousand, nine hundred seventeen".