21681432 has 96 divisors (see below), whose sum is σ = 64209600. Its totient is φ = 6835104.

The previous prime is 21681421. The next prime is 21681449. The reversal of 21681432 is 23418612.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 21681396 and 21681405.

It is a congruent number.

It is an unprimeable number.

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 23 ways as a sum of consecutive naturals, for example, 36643 + ... + 37229.

It is an arithmetic number, because the mean of its divisors is an integer number (668850).

Almost surely, 2^21681432 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 21681432, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32104800).

21681432 is an abundant number, since it is smaller than the sum of its proper divisors (42528168).

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

21681432 is a wasteful number, since it uses less digits than its factorization.

21681432 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 627 (or 611 counting only the distinct ones).

The product of its digits is 2304, while the sum is 27.

The square root of 21681432 is about 4656.3324623570. The cubic root of 21681432 is about 278.8448669307.

It can be divided in two parts, 2168 and 1432, that added together give a square (3600 = 60²).

The spelling of 21681432 in words is "twenty-one million, six hundred eighty-one thousand, four hundred thirty-two".