1661518921 has 2 divisors, whose sum is σ = 1661518922. Its totient is φ = 1661518920.

The previous prime is 1661518879. The next prime is 1661518931. The reversal of 1661518921 is 1298151661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1613146896 + 48372025 = 40164^2 + 6955^2 .

It is an emirp because it is prime and its reverse (1298151661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1661518921 - 2¹³ = 1661510729 is a prime.

It is not a weakly prime, because it can be changed into another prime (1661518931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830759460 + 830759461.

It is an arithmetic number, because the mean of its divisors is an integer number (830759461).

Almost surely, 2^1661518921 is an apocalyptic number.

It is an amenable number.

1661518921 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661518921 is an equidigital number, since it uses as much as digits as its factorization.

1661518921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 25920, while the sum is 40.

The square root of 1661518921 is about 40761.7335377189. The cubic root of 1661518921 is about 1184.4091771277.

The spelling of 1661518921 in words is "one billion, six hundred sixty-one million, five hundred eighteen thousand, nine hundred twenty-one".