81231551 has 2 divisors, whose sum is σ = 81231552. Its totient is φ = 81231550.

The previous prime is 81231509. The next prime is 81231569. The reversal of 81231551 is 15513218.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81231551 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81231551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81231751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40615775 + 40615776.

It is an arithmetic number, because the mean of its divisors is an integer number (40615776).

Almost surely, 2^81231551 is an apocalyptic number.

81231551 is a deficient number, since it is larger than the sum of its proper divisors (1).

81231551 is an equidigital number, since it uses as much as digits as its factorization.

81231551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1200, while the sum is 26.

The square root of 81231551 is about 9012.8547641688. The cubic root of 81231551 is about 433.0867681474.

Adding to 81231551 its reverse (15513218), we get a palindrome (96744769).

The spelling of 81231551 in words is "eighty-one million, two hundred thirty-one thousand, five hundred fifty-one".