1561978081 has 2 divisors, whose sum is σ = 1561978082. Its totient is φ = 1561978080.

The previous prime is 1561978069. The next prime is 1561978109. The reversal of 1561978081 is 1808791651.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1010667681 + 551310400 = 31791^2 + 23480^2 .

It is a cyclic number.

It is not a de Polignac number, because 1561978081 - 2¹¹ = 1561976033 is a prime.

It is a super-2 number, since 2×1561978081² = 4879551051048885122, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1561978021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780989040 + 780989041.

It is an arithmetic number, because the mean of its divisors is an integer number (780989041).

Almost surely, 2^1561978081 is an apocalyptic number.

It is an amenable number.

1561978081 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561978081 is an equidigital number, since it uses as much as digits as its factorization.

1561978081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 120960, while the sum is 46.

The square root of 1561978081 is about 39521.8683895385. The cubic root of 1561978081 is about 1160.2679922334.

The spelling of 1561978081 in words is "one billion, five hundred sixty-one million, nine hundred seventy-eight thousand, eighty-one".