221561816 has 64 divisors (see below), whose sum is σ = 505543680. Its totient is φ = 88865280.

The previous prime is 221561779. The next prime is 221561839. The reversal of 221561816 is 618165122.

221561816 is digitally balanced in base 2 and base 3, because in such bases it contains all the possibile digits an equal number of times.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 200321 + ... + 201423.

It is an arithmetic number, because the mean of its divisors is an integer number (7899120).

Almost surely, 2^221561816 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 221561816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (252771840).

221561816 is an abundant number, since it is smaller than the sum of its proper divisors (283981864).

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

221561816 is a wasteful number, since it uses less digits than its factorization.

221561816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1344 (or 1340 counting only the distinct ones).

The product of its digits is 5760, while the sum is 32.

The square root of 221561816 is about 14884.9526703984. The cubic root of 221561816 is about 605.1062500368.

The spelling of 221561816 in words is "two hundred twenty-one million, five hundred sixty-one thousand, eight hundred sixteen".