81623978291 has 4 divisors (see below), whose sum is σ = 81624550800. Its totient is φ = 81623405784.

The previous prime is 81623978273. The next prime is 81623978323. The reversal of 81623978291 is 19287932618.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 81623978291 - 2¹⁸ = 81623716147 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81623978591) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 116405 + ... + 420473.

It is an arithmetic number, because the mean of its divisors is an integer number (20406137700).

Almost surely, 2^81623978291 is an apocalyptic number.

81623978291 is a deficient number, since it is larger than the sum of its proper divisors (572509).

81623978291 is a wasteful number, since it uses less digits than its factorization.

81623978291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 572508.

The product of its digits is 2612736, while the sum is 56.

The spelling of 81623978291 in words is "eighty-one billion, six hundred twenty-three million, nine hundred seventy-eight thousand, two hundred ninety-one".