21503664 has 160 divisors (see below), whose sum is σ = 76106240. Its totient is φ = 5660928.

The previous prime is 21503653. The next prime is 21503693. The reversal of 21503664 is 46630512.

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

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 39039 + ... + 39585.

It is an arithmetic number, because the mean of its divisors is an integer number (475664).

Almost surely, 2^21503664 is an apocalyptic number.

21503664 is a gapful number since it is divisible by the number (24) 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 21503664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38053120).

21503664 is an abundant number, since it is smaller than the sum of its proper divisors (54602576).

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

21503664 is a wasteful number, since it uses less digits than its factorization.

21503664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 584 (or 572 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 21503664 is about 4637.2043301972. The cubic root of 21503664 is about 278.0806832389.

The spelling of 21503664 in words is "twenty-one million, five hundred three thousand, six hundred sixty-four".