1221705216 has 120 divisors (see below), whose sum is σ = 3601581984. Its totient is φ = 398499840.

The previous prime is 1221705181. The next prime is 1221705229. The reversal of 1221705216 is 6125071221.

1221705216 is a `hidden beast` number, since 122 + 17 + 0 + 521 + 6 = 666.

It is a super-3 number, since 3×1221705216³ (a number of 28 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 1221705216.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 213756 + ... + 219396.

Almost surely, 2^1221705216 is an apocalyptic number.

1221705216 is a gapful number since it is divisible by the number (16) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1221705216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1800790992).

1221705216 is an abundant number, since it is smaller than the sum of its proper divisors (2379876768).

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

1221705216 is an equidigital number, since it uses as much as digits as its factorization.

1221705216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5712 (or 5693 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 1221705216 is about 34952.8999655250. The cubic root of 1221705216 is about 1069.0273328089.

Adding to 1221705216 its reverse (6125071221), we get a palindrome (7346776437).

The spelling of 1221705216 in words is "one billion, two hundred twenty-one million, seven hundred five thousand, two hundred sixteen".