81549491 has 2 divisors, whose sum is σ = 81549492. Its totient is φ = 81549490.

The previous prime is 81549473. The next prime is 81549547. The reversal of 81549491 is 19494518.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81549491 - 2⁶ = 81549427 is a prime.

It is a super-3 number, since 3×81549491³ (a number of 25 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (81549401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40774745 + 40774746.

It is an arithmetic number, because the mean of its divisors is an integer number (40774746).

Almost surely, 2^81549491 is an apocalyptic number.

81549491 is a deficient number, since it is larger than the sum of its proper divisors (1).

81549491 is an equidigital number, since it uses as much as digits as its factorization.

81549491 is an evil number, because the sum of its binary digits is even.

The product of its digits is 51840, while the sum is 41.

The square root of 81549491 is about 9030.4756796085. The cubic root of 81549491 is about 433.6510659204.

The spelling of 81549491 in words is "eighty-one million, five hundred forty-nine thousand, four hundred ninety-one".