81815947 has 2 divisors, whose sum is σ = 81815948. Its totient is φ = 81815946.

The previous prime is 81815897. The next prime is 81815983. The reversal of 81815947 is 74951818.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81815947 - 2¹¹ = 81813899 is a prime.

It is not a weakly prime, because it can be changed into another prime (81810947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40907973 + 40907974.

It is an arithmetic number, because the mean of its divisors is an integer number (40907974).

Almost surely, 2^81815947 is an apocalyptic number.

81815947 is a deficient number, since it is larger than the sum of its proper divisors (1).

81815947 is an equidigital number, since it uses as much as digits as its factorization.

81815947 is an evil number, because the sum of its binary digits is even.

The product of its digits is 80640, while the sum is 43.

The square root of 81815947 is about 9045.2168022663. The cubic root of 81815947 is about 434.1228583914.

The spelling of 81815947 in words is "eighty-one million, eight hundred fifteen thousand, nine hundred forty-seven".