21681064 has 16 divisors (see below), whose sum is σ = 41056020. Its totient is φ = 10732800.

The previous prime is 21681061. The next prime is 21681091. The reversal of 21681064 is 46018612.

It can be written as a sum of positive squares in 2 ways, for example, as 21622500 + 58564 = 4650^2 + 242^2 .

It is not an unprimeable number, because it can be changed into a prime (21681061) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12609 + ... + 14224.

Almost surely, 2^21681064 is an apocalyptic number.

It is an amenable number.

21681064 is a deficient number, since it is larger than the sum of its proper divisors (19374956).

21681064 is a wasteful number, since it uses less digits than its factorization.

21681064 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26940 (or 26936 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 21681064 is about 4656.2929461107. The cubic root of 21681064 is about 278.8432893060.

Adding to 21681064 its reverse (46018612), we get a palindrome (67699676).

The spelling of 21681064 in words is "twenty-one million, six hundred eighty-one thousand, sixty-four".