166121778221128 has 8 divisors (see below), whose sum is σ = 311478334164630. Its totient is φ = 83060889110560.

The previous prime is 166121778221041. The next prime is 166121778221149. The reversal of 166121778221128 is 821122877121661.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 159941094955524 + 6180683265604 = 12646782^2 + 2486098^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a hoax number, since the sum of its digits (55) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10382611138813 + ... + 10382611138828.

Almost surely, 2^{166121778221128} is an apocalyptic number.

It is an amenable number.

166121778221128 is a deficient number, since it is larger than the sum of its proper divisors (145356555943502).

166121778221128 is a wasteful number, since it uses less digits than its factorization.

166121778221128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20765222277647 (or 20765222277643 counting only the distinct ones).

The product of its digits is 1806336, while the sum is 55.

The spelling of 166121778221128 in words is "one hundred sixty-six trillion, one hundred twenty-one billion, seven hundred seventy-eight million, two hundred twenty-one thousand, one hundred twenty-eight".