661020665 has 8 divisors (see below), whose sum is σ = 793919688. Its totient is φ = 528353280.

The previous prime is 661020653. The next prime is 661020671. The reversal of 661020665 is 566020166.

It can be written as a sum of positive squares in 4 ways, for example, as 113273449 + 547747216 = 10643^2 + 23404^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 661020665 - 2¹⁰ = 661019641 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 51566 + ... + 63095.

It is an arithmetic number, because the mean of its divisors is an integer number (99239961).

Almost surely, 2^661020665 is an apocalyptic number.

It is an amenable number.

661020665 is a deficient number, since it is larger than the sum of its proper divisors (132899023).

661020665 is a wasteful number, since it uses less digits than its factorization.

661020665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115819.

The product of its (nonzero) digits is 12960, while the sum is 32.

The square root of 661020665 is about 25710.3221488958. The cubic root of 661020665 is about 871.1073515605.

The spelling of 661020665 in words is "six hundred sixty-one million, twenty thousand, six hundred sixty-five".