81620639 has 2 divisors, whose sum is σ = 81620640. Its totient is φ = 81620638.

The previous prime is 81620633. The next prime is 81620641. The reversal of 81620639 is 93602618.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81620639 - 2¹² = 81616543 is a prime.

Together with 81620641, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 81620599 and 81620608.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81620633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40810319 + 40810320.

It is an arithmetic number, because the mean of its divisors is an integer number (40810320).

Almost surely, 2^81620639 is an apocalyptic number.

81620639 is a deficient number, since it is larger than the sum of its proper divisors (1).

81620639 is an equidigital number, since it uses as much as digits as its factorization.

81620639 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 15552, while the sum is 35.

The square root of 81620639 is about 9034.4141481338. The cubic root of 81620639 is about 433.7771424795. Note that the first 3 decimals are identical.

The spelling of 81620639 in words is "eighty-one million, six hundred twenty thousand, six hundred thirty-nine".