21621264 has 80 divisors (see below), whose sum is σ = 64341120. Its totient is φ = 6128640.

The previous prime is 21621239. The next prime is 21621277. The reversal of 21621264 is 46212612.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a nude number because it is divisible by every one of its digits.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 76804 + ... + 77084.

It is an arithmetic number, because the mean of its divisors is an integer number (804264).

Almost surely, 2^21621264 is an apocalyptic number.

21621264 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 21621264, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32170560).

21621264 is an abundant number, since it is smaller than the sum of its proper divisors (42719856).

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

21621264 is a wasteful number, since it uses less digits than its factorization.

21621264 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 528 (or 522 counting only the distinct ones).

The product of its digits is 1152, while the sum is 24.

The square root of 21621264 is about 4649.8670948749. The cubic root of 21621264 is about 278.5866877713.

Adding to 21621264 its reverse (46212612), we get a palindrome (67833876).

It can be divided in two parts, 21 and 621264, that multiplied together give a square (13046544 = 3612²).

The spelling of 21621264 in words is "twenty-one million, six hundred twenty-one thousand, two hundred sixty-four".