1561971181 has 2 divisors, whose sum is σ = 1561971182. Its totient is φ = 1561971180.

The previous prime is 1561971179. The next prime is 1561971221. The reversal of 1561971181 is 1811791651.

It is an a-pointer prime, because the next prime (1561971221) can be obtained adding 1561971181 to its sum of digits (40).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1485408681 + 76562500 = 38541^2 + 8750^2 .

It is a cyclic number.

It is not a de Polignac number, because 1561971181 - 2¹ = 1561971179 is a prime.

It is a super-2 number, since 2×1561971181² = 4879507940549069522, which contains 22 as substring.

Together with 1561971179, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1561971881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780985590 + 780985591.

It is an arithmetic number, because the mean of its divisors is an integer number (780985591).

Almost surely, 2^1561971181 is an apocalyptic number.

It is an amenable number.

1561971181 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561971181 is an equidigital number, since it uses as much as digits as its factorization.

1561971181 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15120, while the sum is 40.

The square root of 1561971181 is about 39521.7810959982. The cubic root of 1561971181 is about 1160.2662837457.

The spelling of 1561971181 in words is "one billion, five hundred sixty-one million, nine hundred seventy-one thousand, one hundred eighty-one".