21066656 has 48 divisors (see below), whose sum is σ = 45246600. Its totient is φ = 9596928.

The previous prime is 21066641. The next prime is 21066677. The reversal of 21066656 is 65666012.

It can be written as a sum of positive squares in 4 ways, for example, as 7376656 + 13690000 = 2716^2 + 3700^2 .

It is a Harshad number since it is a multiple of its sum of digits (32).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 36740 + ... + 37308.

Almost surely, 2^21066656 is an apocalyptic number.

21066656 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 21066656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22623300).

21066656 is an abundant number, since it is smaller than the sum of its proper divisors (24179944).

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

21066656 is a wasteful number, since it uses less digits than its factorization.

21066656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 681 (or 673 counting only the distinct ones).

The product of its (nonzero) digits is 12960, while the sum is 32.

The square root of 21066656 is about 4589.8426988297. The cubic root of 21066656 is about 276.1840122753.

It can be divided in two parts, 2106 and 6656, that multiplied together give a square (14017536 = 3744²).

The spelling of 21066656 in words is "twenty-one million, sixty-six thousand, six hundred fifty-six".