21506516 has 12 divisors (see below), whose sum is σ = 38934420. Its totient is φ = 10382400.

The previous prime is 21506491. The next prime is 21506519. The reversal of 21506516 is 61560512.

It can be written as a sum of positive squares in 2 ways, for example, as 15523600 + 5982916 = 3940^2 + 2446^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506519) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 92585 + ... + 92816.

It is an arithmetic number, because the mean of its divisors is an integer number (3244535).

Almost surely, 2^21506516 is an apocalyptic number.

It is an amenable number.

21506516 is a deficient number, since it is larger than the sum of its proper divisors (17427904).

21506516 is a wasteful number, since it uses less digits than its factorization.

21506516 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 185434 (or 185432 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21506516 is about 4637.5118328690. The cubic root of 21506516 is about 278.0929765090.

It can be divided in two parts, 21506 and 516, that added together give a palindrome (22022).

The spelling of 21506516 in words is "twenty-one million, five hundred six thousand, five hundred sixteen".