165661261 has 4 divisors (see below), whose sum is σ = 165813372. Its totient is φ = 165509152.

The previous prime is 165661259. The next prime is 165661267. The reversal of 165661261 is 162166561.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17065161 + 148596100 = 4131^2 + 12190^2 .

It is a cyclic number.

It is not a de Polignac number, because 165661261 - 2¹ = 165661259 is a prime.

It is a super-2 number, since 2×165661261² = 54887306792220242, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (165661267) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 74410 + ... + 76603.

It is an arithmetic number, because the mean of its divisors is an integer number (41453343).

Almost surely, 2^165661261 is an apocalyptic number.

It is an amenable number.

165661261 is a deficient number, since it is larger than the sum of its proper divisors (152111).

165661261 is a wasteful number, since it uses less digits than its factorization.

165661261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 152110.

The product of its digits is 12960, while the sum is 34.

The square root of 165661261 is about 12870.9463910002. The cubic root of 165661261 is about 549.2123833914.

The spelling of 165661261 in words is "one hundred sixty-five million, six hundred sixty-one thousand, two hundred sixty-one".