1661518421 has 2 divisors, whose sum is σ = 1661518422. Its totient is φ = 1661518420.

The previous prime is 1661518393. The next prime is 1661518447. The reversal of 1661518421 is 1248151661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1302415921 + 359102500 = 36089^2 + 18950^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661518421 - 2¹⁰ = 1661517397 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661518921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830759210 + 830759211.

It is an arithmetic number, because the mean of its divisors is an integer number (830759211).

Almost surely, 2^1661518421 is an apocalyptic number.

It is an amenable number.

1661518421 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661518421 is an equidigital number, since it uses as much as digits as its factorization.

1661518421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11520, while the sum is 35.

The square root of 1661518421 is about 40761.7274045151. The cubic root of 1661518421 is about 1184.4090583198.

The spelling of 1661518421 in words is "one billion, six hundred sixty-one million, five hundred eighteen thousand, four hundred twenty-one".