21017664 has 56 divisors (see below), whose sum is σ = 61793120. Its totient is φ = 7005312.

The previous prime is 21017657. The next prime is 21017671. The reversal of 21017664 is 46671012.

It is an interprime number because it is at equal distance from previous prime (21017657) and next prime (21017671).

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

It is an unprimeable number.

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 in 7 ways as a sum of consecutive naturals, for example, 4354 + ... + 7809.

Almost surely, 2^21017664 is an apocalyptic number.

21017664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21017664 is an abundant number, since it is smaller than the sum of its proper divisors (40775456).

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

21017664 is a wasteful number, since it uses less digits than its factorization.

21017664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12184 (or 12168 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 27.

The square root of 21017664 is about 4584.5025902490. The cubic root of 21017664 is about 275.9697509382.

Adding to 21017664 its reverse (46671012), we get a palindrome (67688676).

The spelling of 21017664 in words is "twenty-one million, seventeen thousand, six hundred sixty-four".