81542381 has 2 divisors, whose sum is σ = 81542382. Its totient is φ = 81542380.

The previous prime is 81542359. The next prime is 81542393. The reversal of 81542381 is 18324518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 44222500 + 37319881 = 6650^2 + 6109^2 .

It is a cyclic number.

It is not a de Polignac number, because 81542381 - 2¹⁰ = 81541357 is a prime.

It is a super-2 number, since 2×81542381² = 13298319798298322, which contains 22 as substring.

It is equal to p_4754291 and since 81542381 and 4754291 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 (81542341) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40771190 + 40771191.

It is an arithmetic number, because the mean of its divisors is an integer number (40771191).

Almost surely, 2^81542381 is an apocalyptic number.

It is an amenable number.

81542381 is a deficient number, since it is larger than the sum of its proper divisors (1).

81542381 is an equidigital number, since it uses as much as digits as its factorization.

81542381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7680, while the sum is 32.

The square root of 81542381 is about 9030.0820040573. The cubic root of 81542381 is about 433.6384627406.

Adding to 81542381 its reverse (18324518), we get a palindrome (99866899).

The spelling of 81542381 in words is "eighty-one million, five hundred forty-two thousand, three hundred eighty-one".