661320217 has 4 divisors (see below), whose sum is σ = 671190736. Its totient is φ = 651449700.

The previous prime is 661320211. The next prime is 661320223. The reversal of 661320217 is 712023166.

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.

It is an interprime number because it is at equal distance from previous prime (661320211) and next prime (661320223).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661320217 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661320211) 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, 4935159 + ... + 4935292.

It is an arithmetic number, because the mean of its divisors is an integer number (167797684).

Almost surely, 2^661320217 is an apocalyptic number.

661320217 is a gapful number since it is divisible by the number (67) formed by its first and last digit.

It is an amenable number.

661320217 is a deficient number, since it is larger than the sum of its proper divisors (9870519).

661320217 is an equidigital number, since it uses as much as digits as its factorization.

661320217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9870518.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 661320217 is about 25716.1470092236. The cubic root of 661320217 is about 871.2389170604.

The spelling of 661320217 in words is "six hundred sixty-one million, three hundred twenty thousand, two hundred seventeen".