81561049 has 2 divisors, whose sum is σ = 81561050. Its totient is φ = 81561048.

The previous prime is 81561047. The next prime is 81561089. The reversal of 81561049 is 94016518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 73960000 + 7601049 = 8600^2 + 2757^2 .

It is a cyclic number.

It is not a de Polignac number, because 81561049 - 2¹ = 81561047 is a prime.

Together with 81561047, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81561047) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40780524 + 40780525.

It is an arithmetic number, because the mean of its divisors is an integer number (40780525).

Almost surely, 2^81561049 is an apocalyptic number.

It is an amenable number.

81561049 is a deficient number, since it is larger than the sum of its proper divisors (1).

81561049 is an equidigital number, since it uses as much as digits as its factorization.

81561049 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8640, while the sum is 34.

The square root of 81561049 is about 9031.1156010761. The cubic root of 81561049 is about 433.6715520578.

The spelling of 81561049 in words is "eighty-one million, five hundred sixty-one thousand, forty-nine".