1561516661 has 16 divisors (see below), whose sum is σ = 1625315328. Its totient is φ = 1498968000.

The previous prime is 1561516643. The next prime is 1561516681. The reversal of 1561516661 is 1666151651.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1561516661 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 (1561516681) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1430726 + ... + 1431816.

It is an arithmetic number, because the mean of its divisors is an integer number (101582208).

Almost surely, 2^1561516661 is an apocalyptic number.

It is an amenable number.

1561516661 is a deficient number, since it is larger than the sum of its proper divisors (63798667).

1561516661 is a wasteful number, since it uses less digits than its factorization.

1561516661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1612.

The product of its digits is 32400, while the sum is 38.

The square root of 1561516661 is about 39516.0304306999. The cubic root of 1561516661 is about 1160.1537303690.

The spelling of 1561516661 in words is "one billion, five hundred sixty-one million, five hundred sixteen thousand, six hundred sixty-one".