1991557541 has 2 divisors, whose sum is σ = 1991557542. Its totient is φ = 1991557540.

The previous prime is 1991557517. The next prime is 1991557549. The reversal of 1991557541 is 1457551991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1639845025 + 351712516 = 40495^2 + 18754^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991557541 is a prime.

It is a super-2 number, since 2×1991557541² = 7932602878227933362, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991557549) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995778770 + 995778771.

It is an arithmetic number, because the mean of its divisors is an integer number (995778771).

Almost surely, 2^1991557541 is an apocalyptic number.

It is an amenable number.

1991557541 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991557541 is an equidigital number, since it uses as much as digits as its factorization.

1991557541 is an evil number, because the sum of its binary digits is even.

The product of its digits is 283500, while the sum is 47.

The square root of 1991557541 is about 44626.8701680949. The cubic root of 1991557541 is about 1258.1457442547.

The spelling of 1991557541 in words is "one billion, nine hundred ninety-one million, five hundred fifty-seven thousand, five hundred forty-one".