661398145 has 4 divisors (see below), whose sum is σ = 793677780. Its totient is φ = 529118512.

The previous prime is 661398121. The next prime is 661398149. The reversal of 661398145 is 541893166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 541893166 = 2 ⋅270946583.

It can be written as a sum of positive squares in 2 ways, for example, as 516243841 + 145154304 = 22721^2 + 12048^2 .

It is a cyclic number.

It is not a de Polignac number, because 661398145 - 2¹¹ = 661396097 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661398149) 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, 66139810 + ... + 66139819.

It is an arithmetic number, because the mean of its divisors is an integer number (198419445).

Almost surely, 2^661398145 is an apocalyptic number.

It is an amenable number.

661398145 is a deficient number, since it is larger than the sum of its proper divisors (132279635).

661398145 is a wasteful number, since it uses less digits than its factorization.

661398145 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132279634.

The product of its digits is 155520, while the sum is 43.

The square root of 661398145 is about 25717.6621215848. The cubic root of 661398145 is about 871.2731371139.

The spelling of 661398145 in words is "six hundred sixty-one million, three hundred ninety-eight thousand, one hundred forty-five".