1661897651 has 2 divisors, whose sum is σ = 1661897652. Its totient is φ = 1661897650.

The previous prime is 1661897647. The next prime is 1661897689. The reversal of 1661897651 is 1567981661.

It is a weak prime.

It is an emirp because it is prime and its reverse (1567981661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1661897651 - 2² = 1661897647 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1661897651.

It is not a weakly prime, because it can be changed into another prime (1661897351) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830948825 + 830948826.

It is an arithmetic number, because the mean of its divisors is an integer number (830948826).

Almost surely, 2^1661897651 is an apocalyptic number.

1661897651 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661897651 is an equidigital number, since it uses as much as digits as its factorization.

1661897651 is an evil number, because the sum of its binary digits is even.

The product of its digits is 544320, while the sum is 50.

The square root of 1661897651 is about 40766.3789292108. The cubic root of 1661897651 is about 1184.4991625026.

The spelling of 1661897651 in words is "one billion, six hundred sixty-one million, eight hundred ninety-seven thousand, six hundred fifty-one".