72181661 has 4 divisors (see below), whose sum is σ = 72234300. Its totient is φ = 72129024.

The previous prime is 72181631. The next prime is 72181691. The reversal of 72181661 is 16618127.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16618127 = 367 ⋅45281.

It is an interprime number because it is at equal distance from previous prime (72181631) and next prime (72181691).

It can be written as a sum of positive squares in 2 ways, for example, as 5040025 + 67141636 = 2245^2 + 8194^2 .

It is a cyclic number.

It is not a de Polignac number, because 72181661 - 2¹⁰ = 72180637 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (72181621) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 24206 + ... + 27023.

It is an arithmetic number, because the mean of its divisors is an integer number (18058575).

Almost surely, 2^72181661 is an apocalyptic number.

It is an amenable number.

72181661 is a deficient number, since it is larger than the sum of its proper divisors (52639).

72181661 is a wasteful number, since it uses less digits than its factorization.

72181661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52638.

The product of its digits is 4032, while the sum is 32.

The square root of 72181661 is about 8495.9791077898. The cubic root of 72181661 is about 416.3663504943.

Adding to 72181661 its reverse (16618127), we get a palindrome (88799788).

The spelling of 72181661 in words is "seventy-two million, one hundred eighty-one thousand, six hundred sixty-one".