21551616 has 80 divisors (see below), whose sum is σ = 63835200. Its totient is φ = 7179264.

The previous prime is 21551591. The next prime is 21551623. The reversal of 21551616 is 61615512.

It is a happy number.

It is a super-2 number, since 2×21551616² = 928944304422912, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a self number, because there is not a number n which added to its sum of digits gives 21551616.

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, 13045 + ... + 14603.

It is an arithmetic number, because the mean of its divisors is an integer number (797940).

Almost surely, 2^21551616 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 21551616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31917600).

21551616 is an abundant number, since it is smaller than the sum of its proper divisors (42283584).

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

21551616 is an equidigital number, since it uses as much as digits as its factorization.

21551616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1586 (or 1564 counting only the distinct ones).

The product of its digits is 1800, while the sum is 27.

The square root of 21551616 is about 4642.3718076001. The cubic root of 21551616 is about 278.2872313793.

The spelling of 21551616 in words is "twenty-one million, five hundred fifty-one thousand, six hundred sixteen".