15681640 has 64 divisors (see below), whose sum is σ = 38782800. Its totient is φ = 5670912.

The previous prime is 15681623. The next prime is 15681643. The reversal of 15681640 is 4618651.

15681640 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 8 ways, for example, as 2965284 + 12716356 = 1722^2 + 3566^2 .

It is not an unprimeable number, because it can be changed into a prime (15681643) 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, 27276 + ... + 27844.

Almost surely, 2^15681640 is an apocalyptic number.

15681640 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 15681640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (19391400).

15681640 is an abundant number, since it is smaller than the sum of its proper divisors (23101160).

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

15681640 is a wasteful number, since it uses less digits than its factorization.

15681640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 646 (or 642 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 31.

The square root of 15681640 is about 3960.0050505018. The cubic root of 15681640 is about 250.3017157240.

It can be divided in two parts, 156 and 81640, that added together give a square (81796 = 286²).

The spelling of 15681640 in words is "fifteen million, six hundred eighty-one thousand, six hundred forty".