1555647991 has 2 divisors, whose sum is σ = 1555647992. Its totient is φ = 1555647990.

The previous prime is 1555647979. The next prime is 1555648043. The reversal of 1555647991 is 1997465551.

It is an a-pointer prime, because the next prime (1555648043) can be obtained adding 1555647991 to its sum of digits (52).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1555647991 - 2⁵ = 1555647959 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1555647901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 777823995 + 777823996.

It is an arithmetic number, because the mean of its divisors is an integer number (777823996).

Almost surely, 2^1555647991 is an apocalyptic number.

1555647991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1555647991 is an equidigital number, since it uses as much as digits as its factorization.

1555647991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1701000, while the sum is 52.

The square root of 1555647991 is about 39441.7037030603. The cubic root of 1555647991 is about 1158.6984984172.

The spelling of 1555647991 in words is "one billion, five hundred fifty-five million, six hundred forty-seven thousand, nine hundred ninety-one".