81503581 has 2 divisors, whose sum is σ = 81503582. Its totient is φ = 81503580.

The previous prime is 81503579. The next prime is 81503621. The reversal of 81503581 is 18530518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 77264100 + 4239481 = 8790^2 + 2059^2 .

It is a cyclic number.

It is not a de Polignac number, because 81503581 - 2¹ = 81503579 is a prime.

It is a super-2 number, since 2×81503581² = 13285667431647122, which contains 22 as substring.

Together with 81503579, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81507581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40751790 + 40751791.

It is an arithmetic number, because the mean of its divisors is an integer number (40751791).

Almost surely, 2^81503581 is an apocalyptic number.

It is an amenable number.

81503581 is a deficient number, since it is larger than the sum of its proper divisors (1).

81503581 is an equidigital number, since it uses as much as digits as its factorization.

81503581 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4800, while the sum is 31.

The square root of 81503581 is about 9027.9333737019. The cubic root of 81503581 is about 433.5696729838.

The spelling of 81503581 in words is "eighty-one million, five hundred three thousand, five hundred eighty-one".