1661516221 has 2 divisors, whose sum is σ = 1661516222. Its totient is φ = 1661516220.

The previous prime is 1661516203. The next prime is 1661516257. The reversal of 1661516221 is 1226151661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1123925625 + 537590596 = 33525^2 + 23186^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661516221 - 2⁷ = 1661516093 is a prime.

It is a super-2 number, since 2×1661516221² = 5521272305292241682, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661516621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830758110 + 830758111.

It is an arithmetic number, because the mean of its divisors is an integer number (830758111).

Almost surely, 2^1661516221 is an apocalyptic number.

It is an amenable number.

1661516221 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661516221 is an equidigital number, since it uses as much as digits as its factorization.

1661516221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4320, while the sum is 31.

The square root of 1661516221 is about 40761.7004184075. The cubic root of 1661516221 is about 1184.4085355648.

Adding to 1661516221 its reverse (1226151661), we get a palindrome (2887667882).

The spelling of 1661516221 in words is "one billion, six hundred sixty-one million, five hundred sixteen thousand, two hundred twenty-one".