661666517 has 4 divisors (see below), whose sum is σ = 675744576. Its totient is φ = 647588460.

The previous prime is 661666513. The next prime is 661666529. The reversal of 661666517 is 715666166.

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 an emirpimes, since its reverse is a distinct semiprime: 715666166 = 2 ⋅357833083.

It is a cyclic number.

It is not a de Polignac number, because 661666517 - 2² = 661666513 is a prime.

It is a super-2 number, since 2×661666517² = 875605159437822578, 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 (661666513) 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, 7038959 + ... + 7039052.

It is an arithmetic number, because the mean of its divisors is an integer number (168936144).

Almost surely, 2^661666517 is an apocalyptic number.

It is an amenable number.

661666517 is a deficient number, since it is larger than the sum of its proper divisors (14078059).

661666517 is a wasteful number, since it uses less digits than its factorization.

661666517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14078058.

The product of its digits is 272160, while the sum is 44.

The square root of 661666517 is about 25722.8792517478. The cubic root of 661666517 is about 871.3909651308.

The spelling of 661666517 in words is "six hundred sixty-one million, six hundred sixty-six thousand, five hundred seventeen".