1661221965456 has 135 divisors (see below), whose sum is σ = 4907551039209. Its totient is φ = 524503610496.

The previous prime is 1661221965451. The next prime is 1661221965463. The reversal of 1661221965456 is 6545691221661.

It is a happy number.

The square root of 1661221965456 is 1288884.

It is a perfect power (a square), and thus also a powerful number.

1661221965456 is a `hidden beast` number, since 1 + 6 + 6 + 1 + 2 + 2 + 1 + 96 + 545 + 6 = 666.

It can be written as a sum of positive squares in only one way, i.e., 1302200499600 + 359021465856 = 1141140^2 + 599184^2 .

It is not an unprimeable number, because it can be changed into a prime (1661221965451) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 293862726 + ... + 293868378.

Almost surely, 2^{1661221965456} is an apocalyptic number.

1661221965456 is a gapful number since it is divisible by the number (16) formed by its first and last digit.

1661221965456 is the 1288884-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1661221965456

1661221965456 is an abundant number, since it is smaller than the sum of its proper divisors (3246329073753).

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

1661221965456 is an frugal number, since it uses more digits than its factorization.

1661221965456 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11358 (or 5677 counting only the distinct ones).

The product of its digits is 4665600, while the sum is 54.

The spelling of 1661221965456 in words is "one trillion, six hundred sixty-one billion, two hundred twenty-one million, nine hundred sixty-five thousand, four hundred fifty-six".