81506121491 has 2 divisors, whose sum is σ = 81506121492. Its totient is φ = 81506121490.

The previous prime is 81506121467. The next prime is 81506121493. The reversal of 81506121491 is 19412160518.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81506121491 - 2¹⁰ = 81506120467 is a prime.

Together with 81506121493, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81506121493) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40753060745 + 40753060746.

It is an arithmetic number, because the mean of its divisors is an integer number (40753060746).

Almost surely, 2^81506121491 is an apocalyptic number.

81506121491 is a deficient number, since it is larger than the sum of its proper divisors (1).

81506121491 is an equidigital number, since it uses as much as digits as its factorization.

81506121491 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 17280, while the sum is 38.

The spelling of 81506121491 in words is "eighty-one billion, five hundred six million, one hundred twenty-one thousand, four hundred ninety-one".