21666736 has 80 divisors (see below), whose sum is σ = 53996544. Its totient is φ = 8186112.

The previous prime is 21666731. The next prime is 21666739. The reversal of 21666736 is 63766612.

It is a junction number, because it is equal to n+sod(n) for n = 21666695 and 21666704.

It is not an unprimeable number, because it can be changed into a prime (21666731) 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, 33165 + ... + 33811.

Almost surely, 2^21666736 is an apocalyptic number.

21666736 is a gapful number since it is divisible by the number (26) 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 21666736, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26998272).

21666736 is an abundant number, since it is smaller than the sum of its proper divisors (32329808).

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

21666736 is a wasteful number, since it uses less digits than its factorization.

21666736 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 698 (or 692 counting only the distinct ones).

The product of its digits is 54432, while the sum is 37.

The square root of 21666736 is about 4654.7541288450. The cubic root of 21666736 is about 278.7818509456.

The spelling of 21666736 in words is "twenty-one million, six hundred sixty-six thousand, seven hundred thirty-six".