81511237 has 2 divisors, whose sum is σ = 81511238. Its totient is φ = 81511236.

The previous prime is 81511231. The next prime is 81511249. The reversal of 81511237 is 73211518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 65302561 + 16208676 = 8081^2 + 4026^2 .

It is a cyclic number.

It is not a de Polignac number, because 81511237 - 2²³ = 73122629 is a prime.

It is equal to p_4752622 and since 81511237 and 4752622 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81511231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40755618 + 40755619.

It is an arithmetic number, because the mean of its divisors is an integer number (40755619).

Almost surely, 2^81511237 is an apocalyptic number.

It is an amenable number.

81511237 is a deficient number, since it is larger than the sum of its proper divisors (1).

81511237 is an equidigital number, since it uses as much as digits as its factorization.

81511237 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1680, while the sum is 28.

The square root of 81511237 is about 9028.3573810522. The cubic root of 81511237 is about 433.5832482788.

The spelling of 81511237 in words is "eighty-one million, five hundred eleven thousand, two hundred thirty-seven".