647205811661 has 4 divisors (see below), whose sum is σ = 649273562172. Its totient is φ = 645138061152.

The previous prime is 647205811657. The next prime is 647205811669. The reversal of 647205811661 is 166118502746.

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 205838245636 + 441367566025 = 453694^2 + 664355^2 .

It is a cyclic number.

It is not a de Polignac number, because 647205811661 - 2² = 647205811657 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 (647205811669) 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, 1033874786 + ... + 1033875411.

It is an arithmetic number, because the mean of its divisors is an integer number (162318390543).

Almost surely, 2^647205811661 is an apocalyptic number.

It is an amenable number.

647205811661 is a deficient number, since it is larger than the sum of its proper divisors (2067750511).

647205811661 is a wasteful number, since it uses less digits than its factorization.

647205811661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2067750510.

The product of its (nonzero) digits is 483840, while the sum is 47.

The spelling of 647205811661 in words is "six hundred forty-seven billion, two hundred five million, eight hundred eleven thousand, six hundred sixty-one".