391951561 has 4 divisors (see below), whose sum is σ = 393408900. Its totient is φ = 390494224.

The previous prime is 391951537. The next prime is 391951577. The reversal of 391951561 is 165159193.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165159193 = 41 ⋅4028273.

It can be written as a sum of positive squares in 2 ways, for example, as 7595536 + 384356025 = 2756^2 + 19605^2 .

It is a cyclic number.

It is not a de Polignac number, because 391951561 - 2¹¹ = 391949513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (391951531) 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, 728266 + ... + 728803.

It is an arithmetic number, because the mean of its divisors is an integer number (98352225).

Almost surely, 2^391951561 is an apocalyptic number.

It is an amenable number.

391951561 is a deficient number, since it is larger than the sum of its proper divisors (1457339).

391951561 is a wasteful number, since it uses less digits than its factorization.

391951561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1457338.

The product of its digits is 36450, while the sum is 40.

The square root of 391951561 is about 19797.7665659538. The cubic root of 391951561 is about 731.8309956762.

The spelling of 391951561 in words is "three hundred ninety-one million, nine hundred fifty-one thousand, five hundred sixty-one".