19718981 has 4 divisors (see below), whose sum is σ = 20576352. Its totient is φ = 18861612.

The previous prime is 19718977. The next prime is 19718989. The reversal of 19718981 is 18981791.

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 19718981 - 2² = 19718977 is a prime.

It is a super-2 number, since 2×19718981² = 777676423356722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19718989) 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, 428651 + ... + 428696.

It is an arithmetic number, because the mean of its divisors is an integer number (5144088).

Almost surely, 2^19718981 is an apocalyptic number.

It is an amenable number.

19718981 is a deficient number, since it is larger than the sum of its proper divisors (857371).

19718981 is an equidigital number, since it uses as much as digits as its factorization.

19718981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 857370.

The product of its digits is 36288, while the sum is 44.

The square root of 19718981 is about 4440.6059271230. The cubic root of 19718981 is about 270.1644220280.

The spelling of 19718981 in words is "nineteen million, seven hundred eighteen thousand, nine hundred eighty-one".