19971640 has 64 divisors (see below), whose sum is σ = 48888000. Its totient is φ = 7299072.

The previous prime is 19971607. The next prime is 19971643. The reversal of 19971640 is 4617991.

It is a self number, because there is not a number n which added to its sum of digits gives 19971640.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19971643) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 100261 + ... + 100459.

It is an arithmetic number, because the mean of its divisors is an integer number (763875).

Almost surely, 2^19971640 is an apocalyptic number.

19971640 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 19971640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24444000).

19971640 is an abundant number, since it is smaller than the sum of its proper divisors (28916360).

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

19971640 is a wasteful number, since it uses less digits than its factorization.

19971640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 416 (or 412 counting only the distinct ones).

The product of its (nonzero) digits is 13608, while the sum is 37.

The square root of 19971640 is about 4468.9640857810. The cubic root of 19971640 is about 271.3133994952.

The spelling of 19971640 in words is "nineteen million, nine hundred seventy-one thousand, six hundred forty".