21506464 has 48 divisors (see below), whose sum is σ = 49146048. Its totient is φ = 9073152.

The previous prime is 21506453. The next prime is 21506473. The reversal of 21506464 is 46460512.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

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, 14292 + ... + 15724.

It is an arithmetic number, because the mean of its divisors is an integer number (1023876).

Almost surely, 2^21506464 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21506464, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24573024).

21506464 is an abundant number, since it is smaller than the sum of its proper divisors (27639584).

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

21506464 is a wasteful number, since it uses less digits than its factorization.

21506464 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1517 (or 1509 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 28.

The square root of 21506464 is about 4637.5062264109. The cubic root of 21506464 is about 278.0927523778.

Adding to 21506464 its reverse (46460512), we get a palindrome (67966976).

The spelling of 21506464 in words is "twenty-one million, five hundred six thousand, four hundred sixty-four".