6601781561 has 4 divisors (see below), whose sum is σ = 6602160372. Its totient is φ = 6601402752.

The previous prime is 6601781533. The next prime is 6601781579. The reversal of 6601781561 is 1651871066.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1651871066 = 2 ⋅825935533.

It can be written as a sum of positive squares in 2 ways, for example, as 1813141561 + 4788640000 = 42581^2 + 69200^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6601781561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6601781521) 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, 161936 + ... + 198561.

It is an arithmetic number, because the mean of its divisors is an integer number (1650540093).

Almost surely, 2^6601781561 is an apocalyptic number.

It is an amenable number.

6601781561 is a deficient number, since it is larger than the sum of its proper divisors (378811).

6601781561 is a wasteful number, since it uses less digits than its factorization.

6601781561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 378810.

The product of its (nonzero) digits is 60480, while the sum is 41.

The square root of 6601781561 is about 81251.3480565092. The cubic root of 6601781561 is about 1875.9462185646.

The spelling of 6601781561 in words is "six billion, six hundred one million, seven hundred eighty-one thousand, five hundred sixty-one".