81491569 has 2 divisors, whose sum is σ = 81491570. Its totient is φ = 81491568.

The previous prime is 81491519. The next prime is 81491593. The reversal of 81491569 is 96519418.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 67897600 + 13593969 = 8240^2 + 3687^2 .

It is a cyclic number.

It is not a de Polignac number, because 81491569 - 2¹³ = 81483377 is a prime.

It is a super-4 number, since 4×81491569⁴ (a number of 33 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is not a weakly prime, because it can be changed into another prime (81491519) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40745784 + 40745785.

It is an arithmetic number, because the mean of its divisors is an integer number (40745785).

Almost surely, 2^81491569 is an apocalyptic number.

It is an amenable number.

81491569 is a deficient number, since it is larger than the sum of its proper divisors (1).

81491569 is an equidigital number, since it uses as much as digits as its factorization.

81491569 is an evil number, because the sum of its binary digits is even.

The product of its digits is 77760, while the sum is 43.

The square root of 81491569 is about 9027.2680806543. The cubic root of 81491569 is about 433.5483721005.

The spelling of 81491569 in words is "eighty-one million, four hundred ninety-one thousand, five hundred sixty-nine".