661665155 has 4 divisors (see below), whose sum is σ = 793998192. Its totient is φ = 529332120.

The previous prime is 661665113. The next prime is 661665157. The reversal of 661665155 is 551566166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 551566166 = 2 ⋅275783083.

It is not a de Polignac number, because 661665155 - 2¹² = 661661059 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661665157) 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, 66166511 + ... + 66166520.

It is an arithmetic number, because the mean of its divisors is an integer number (198499548).

Almost surely, 2^661665155 is an apocalyptic number.

661665155 is a deficient number, since it is larger than the sum of its proper divisors (132333037).

661665155 is a wasteful number, since it uses less digits than its factorization.

661665155 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132333036.

The product of its digits is 162000, while the sum is 41.

The square root of 661665155 is about 25722.8527772485. The cubic root of 661665155 is about 871.3903672288.

The spelling of 661665155 in words is "six hundred sixty-one million, six hundred sixty-five thousand, one hundred fifty-five".