21147664 has 10 divisors (see below), whose sum is σ = 40973630. Its totient is φ = 10573824.

The previous prime is 21147661. The next prime is 21147667. The reversal of 21147664 is 46674112.

It is an interprime number because it is at equal distance from previous prime (21147661) and next prime (21147667).

It can be written as a sum of positive squares in only one way, i.e., 13749264 + 7398400 = 3708^2 + 2720^2 .

It is not an unprimeable number, because it can be changed into a prime (21147661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 660849 + ... + 660880.

It is an arithmetic number, because the mean of its divisors is an integer number (4097363).

Almost surely, 2^21147664 is an apocalyptic number.

It is an amenable number.

21147664 is a deficient number, since it is larger than the sum of its proper divisors (19825966).

21147664 is a wasteful number, since it uses less digits than its factorization.

21147664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1321737 (or 1321731 counting only the distinct ones).

The product of its digits is 8064, while the sum is 31.

The square root of 21147664 is about 4598.6589349505. The cubic root of 21147664 is about 276.5375646430.

The spelling of 21147664 in words is "twenty-one million, one hundred forty-seven thousand, six hundred sixty-four".