19991557 has 2 divisors, whose sum is σ = 19991558. Its totient is φ = 19991556.

The previous prime is 19991551. The next prime is 19991563. The reversal of 19991557 is 75519991.

It is a balanced prime because it is at equal distance from previous prime (19991551) and next prime (19991563).

It can be written as a sum of positive squares in only one way, i.e., 13771521 + 6220036 = 3711^2 + 2494^2 .

It is a cyclic number.

It is not a de Polignac number, because 19991557 - 2³ = 19991549 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19991551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9995778 + 9995779.

It is an arithmetic number, because the mean of its divisors is an integer number (9995779).

Almost surely, 2^19991557 is an apocalyptic number.

It is an amenable number.

19991557 is a deficient number, since it is larger than the sum of its proper divisors (1).

19991557 is an equidigital number, since it uses as much as digits as its factorization.

19991557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 127575, while the sum is 46.

The square root of 19991557 is about 4471.1918992591. The cubic root of 19991557 is about 271.4035599035.

The spelling of 19991557 in words is "nineteen million, nine hundred ninety-one thousand, five hundred fifty-seven".