1661491571 has 2 divisors, whose sum is σ = 1661491572. Its totient is φ = 1661491570.

The previous prime is 1661491567. The next prime is 1661491621. The reversal of 1661491571 is 1751941661.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1661491571 - 2² = 1661491567 is a prime.

It is not a weakly prime, because it can be changed into another prime (1661491561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830745785 + 830745786.

It is an arithmetic number, because the mean of its divisors is an integer number (830745786).

Almost surely, 2^1661491571 is an apocalyptic number.

1661491571 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661491571 is an equidigital number, since it uses as much as digits as its factorization.

1661491571 is an evil number, because the sum of its binary digits is even.

The product of its digits is 45360, while the sum is 41.

The square root of 1661491571 is about 40761.3980501160. The cubic root of 1661491571 is about 1184.4026783014.

The spelling of 1661491571 in words is "one billion, six hundred sixty-one million, four hundred ninety-one thousand, five hundred seventy-one".