55581991 has 2 divisors, whose sum is σ = 55581992. Its totient is φ = 55581990.

The previous prime is 55581979. The next prime is 55581997. The reversal of 55581991 is 19918555.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 55581991 - 2¹¹ = 55579943 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (55581997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 27790995 + 27790996.

It is an arithmetic number, because the mean of its divisors is an integer number (27790996).

Almost surely, 2^55581991 is an apocalyptic number.

55581991 is a deficient number, since it is larger than the sum of its proper divisors (1).

55581991 is an equidigital number, since it uses as much as digits as its factorization.

55581991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 81000, while the sum is 43.

The square root of 55581991 is about 7455.3330576172. Note that the first 3 decimals coincide. The cubic root of 55581991 is about 381.6319266469.

The spelling of 55581991 in words is "fifty-five million, five hundred eighty-one thousand, nine hundred ninety-one".