19997981 has 8 divisors (see below), whose sum is σ = 20388480. Its totient is φ = 19611072.

The previous prime is 19997963. The next prime is 19997993. The reversal of 19997981 is 18979991.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19997981 is a prime.

It is a super-3 number, since 3×19997981³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19997911) 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, 12101 + ... + 13653.

It is an arithmetic number, because the mean of its divisors is an integer number (2548560).

Almost surely, 2^19997981 is an apocalyptic number.

It is an amenable number.

19997981 is a deficient number, since it is larger than the sum of its proper divisors (390499).

19997981 is a wasteful number, since it uses less digits than its factorization.

19997981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1795.

The product of its digits is 367416, while the sum is 53.

The square root of 19997981 is about 4471.9102182401. The cubic root of 19997981 is about 271.4326273368.

The spelling of 19997981 in words is "nineteen million, nine hundred ninety-seven thousand, nine hundred eighty-one".