21251616 has 96 divisors (see below), whose sum is σ = 59447808. Its totient is φ = 6635520.

The previous prime is 21251611. The next prime is 21251617. The reversal of 21251616 is 61615212.

It is a tau number, because it is divible by the number of its divisors (96).

It is a super-2 number, since 2×21251616² = 903262365222912, which contains 22 as substring.

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

It is not an unprimeable number, because it can be changed into a prime (21251611) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 110016 + ... + 110208.

It is an arithmetic number, because the mean of its divisors is an integer number (619248).

Almost surely, 2^21251616 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 21251616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29723904).

21251616 is an abundant number, since it is smaller than the sum of its proper divisors (38196192).

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

21251616 is a wasteful number, since it uses less digits than its factorization.

21251616 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 274 (or 266 counting only the distinct ones).

The product of its digits is 720, while the sum is 24.

The square root of 21251616 is about 4609.9475051241. The cubic root of 21251616 is about 276.9899339050.

Adding to 21251616 its reverse (61615212), we get a palindrome (82866828).

It can be divided in two parts, 2125 and 1616, that added together give a triangular number (3741 = T₈₆).

The spelling of 21251616 in words is "twenty-one million, two hundred fifty-one thousand, six hundred sixteen".