81621559 has 2 divisors, whose sum is σ = 81621560. Its totient is φ = 81621558.

The previous prime is 81621541. The next prime is 81621581. The reversal of 81621559 is 95512618.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81621559 - 2¹⁵ = 81588791 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81621509) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40810779 + 40810780.

It is an arithmetic number, because the mean of its divisors is an integer number (40810780).

Almost surely, 2^81621559 is an apocalyptic number.

81621559 is a deficient number, since it is larger than the sum of its proper divisors (1).

81621559 is an equidigital number, since it uses as much as digits as its factorization.

81621559 is an evil number, because the sum of its binary digits is even.

The product of its digits is 21600, while the sum is 37.

The square root of 81621559 is about 9034.4650644075. The cubic root of 81621559 is about 433.7787722694.

The spelling of 81621559 in words is "eighty-one million, six hundred twenty-one thousand, five hundred fifty-nine".