21561264 has 30 divisors (see below), whose sum is σ = 60341996. Its totient is φ = 7187040.

The previous prime is 21561251. The next prime is 21561277. The reversal of 21561264 is 46216512.

It is an interprime number because it is at equal distance from previous prime (21561251) and next prime (21561277).

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 74722 + ... + 75009.

Almost surely, 2^21561264 is an apocalyptic number.

21561264 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21561264 is an abundant number, since it is smaller than the sum of its proper divisors (38780732).

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

21561264 is a wasteful number, since it uses less digits than its factorization.

21561264 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 149745 (or 149736 counting only the distinct ones).

The product of its digits is 2880, while the sum is 27.

The square root of 21561264 is about 4643.4108153382. The cubic root of 21561264 is about 278.3287520810.

Adding to 21561264 its reverse (46216512), we get a palindrome (67777776).

The spelling of 21561264 in words is "twenty-one million, five hundred sixty-one thousand, two hundred sixty-four".