1561967681 has 2 divisors, whose sum is σ = 1561967682. Its totient is φ = 1561967680.

The previous prime is 1561967669. The next prime is 1561967689. The reversal of 1561967681 is 1867691651.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1365967681 + 196000000 = 36959^2 + 14000^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1561967681 is a prime.

It is a super-2 number, since 2×1561967681² = 4879486072977035522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1561967689) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780983840 + 780983841.

It is an arithmetic number, because the mean of its divisors is an integer number (780983841).

Almost surely, 2^1561967681 is an apocalyptic number.

It is an amenable number.

1561967681 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561967681 is an equidigital number, since it uses as much as digits as its factorization.

1561967681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 544320, while the sum is 50.

The square root of 1561967681 is about 39521.7368165925. The cubic root of 1561967681 is about 1160.2654171196.

The spelling of 1561967681 in words is "one billion, five hundred sixty-one million, nine hundred sixty-seven thousand, six hundred eighty-one".