21515216 has 40 divisors (see below), whose sum is σ = 43691400. Its totient is φ = 10250240.

The previous prime is 21515203. The next prime is 21515227. The reversal of 21515216 is 61251512.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 355216 + 21160000 = 596^2 + 4600^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21515191 and 21515200.

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, 41036 + ... + 41556.

It is an arithmetic number, because the mean of its divisors is an integer number (1092285).

Almost surely, 2^21515216 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 21515216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21845700).

21515216 is an abundant number, since it is smaller than the sum of its proper divisors (22176184).

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

21515216 is a wasteful number, since it uses less digits than its factorization.

21515216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 647 (or 641 counting only the distinct ones).

The product of its digits is 600, while the sum is 23.

The square root of 21515216 is about 4638.4497410234. The cubic root of 21515216 is about 278.1304703044.

Adding to 21515216 its reverse (61251512), we get a palindrome (82766728).

The spelling of 21515216 in words is "twenty-one million, five hundred fifteen thousand, two hundred sixteen".