164121721 has 9 divisors (see below), whose sum is σ = 171876271. Its totient is φ = 156704152.

The previous prime is 164121709. The next prime is 164121733. The reversal of 164121721 is 127121461.

The square root of 164121721 is 12811.

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

It is an interprime number because it is at equal distance from previous prime (164121709) and next prime (164121733).

It can be written as a sum of positive squares in only one way, i.e., 14402025 + 149719696 = 3795^2 + 12236^2 .

It is a de Polignac number, because none of the positive numbers 2^k-164121721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (164121521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 294375 + ... + 294931.

Almost surely, 2^164121721 is an apocalyptic number.

164121721 is the 12811-st square number.

164121721 is the 6406-th centered octagonal number.

It is an amenable number.

164121721 is a deficient number, since it is larger than the sum of its proper divisors (7754550).

164121721 is an frugal number, since it uses more digits than its factorization.

164121721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1160 (or 580 counting only the distinct ones).

The product of its digits is 672, while the sum is 25.

The cubic root of 164121721 is about 547.5057536422.

Multiplying 164121721 by its sum of digits (25), we get a square (4103043025 = 64055²).

The spelling of 164121721 in words is "one hundred sixty-four million, one hundred twenty-one thousand, seven hundred twenty-one".