1221329664 has 216 divisors, whose sum is σ = 3783321360. Its totient is φ = 392491008.

The previous prime is 1221329653. The next prime is 1221329687. The reversal of 1221329664 is 4669231221.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (216).

It is a super-2 number, since 2×1221329664² = 2983292296332705792, which contains 22 as substring.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits and also a Zuckerman number because it is divisible by the product of its digits.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1803694 + ... + 1804370.

Almost surely, 2^1221329664 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 1221329664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1891660680).

1221329664 is an abundant number, since it is smaller than the sum of its proper divisors (2561991696).

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

1221329664 is an frugal number, since it uses more digits than its factorization.

1221329664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 737 (or 711 counting only the distinct ones).

The product of its digits is 31104, while the sum is 36.

The square root of 1221329664 is about 34947.5272945025. The cubic root of 1221329664 is about 1068.9177819690.

The spelling of 1221329664 in words is "one billion, two hundred twenty-one million, three hundred twenty-nine thousand, six hundred sixty-four".