661991487257 has 4 divisors (see below), whose sum is σ = 700932162996. Its totient is φ = 623050811520.

The previous prime is 661991487239. The next prime is 661991487307. The reversal of 661991487257 is 752784199166.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 268180015321 + 393811471936 = 517861^2 + 627544^2 .

It is a cyclic number.

It is not a de Polignac number, because 661991487257 - 2¹² = 661991483161 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 661991487193 and 661991487202.

It is not an unprimeable number, because it can be changed into a prime (661991487217) 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, 19470337844 + ... + 19470337877.

It is an arithmetic number, because the mean of its divisors is an integer number (175233040749).

Almost surely, 2^661991487257 is an apocalyptic number.

It is an amenable number.

661991487257 is a deficient number, since it is larger than the sum of its proper divisors (38940675739).

661991487257 is a wasteful number, since it uses less digits than its factorization.

661991487257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38940675738.

The product of its digits is 45722880, while the sum is 65.

The spelling of 661991487257 in words is "six hundred sixty-one billion, nine hundred ninety-one million, four hundred eighty-seven thousand, two hundred fifty-seven".