661857253 has 4 divisors (see below), whose sum is σ = 661910560. Its totient is φ = 661803948.

The previous prime is 661857233. The next prime is 661857271. The reversal of 661857253 is 352758166.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 352758166 = 2 ⋅176379083.

It is a cyclic number.

It is not a de Polignac number, because 661857253 - 2¹⁷ = 661726181 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 (661857233) 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, 2878 + ... + 36496.

It is an arithmetic number, because the mean of its divisors is an integer number (165477640).

Almost surely, 2^661857253 is an apocalyptic number.

It is an amenable number.

661857253 is a deficient number, since it is larger than the sum of its proper divisors (53307).

661857253 is a wasteful number, since it uses less digits than its factorization.

661857253 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53306.

The product of its digits is 302400, while the sum is 43.

The square root of 661857253 is about 25726.5865011276. The cubic root of 661857253 is about 871.4746879000.

The spelling of 661857253 in words is "six hundred sixty-one million, eight hundred fifty-seven thousand, two hundred fifty-three".