19971684 has 54 divisors (see below), whose sum is σ = 52491894. Its totient is φ = 6648480.

The previous prime is 19971683. The next prime is 19971739. The reversal of 19971684 is 48617991.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 10497600 + 9474084 = 3240^2 + 3078^2 .

It is a tau number, because it is divible by the number of its divisors (54).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19971683) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 25864 + ... + 26624.

Almost surely, 2^19971684 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 19971684, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26245947).

19971684 is an abundant number, since it is smaller than the sum of its proper divisors (32520210).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

19971684 is an frugal number, since it uses more digits than its factorization.

19971684 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 789 (or 766 counting only the distinct ones).

The product of its digits is 108864, while the sum is 45.

The square root of 19971684 is about 4468.9690086193. The cubic root of 19971684 is about 271.3135987407.

The spelling of 19971684 in words is "nineteen million, nine hundred seventy-one thousand, six hundred eighty-four".