1321621661 has 2 divisors, whose sum is σ = 1321621662. Its totient is φ = 1321621660.

The previous prime is 1321621657. The next prime is 1321621673. The reversal of 1321621661 is 1661261231.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1272705625 + 48916036 = 35675^2 + 6994^2 .

It is a cyclic number.

It is not a de Polignac number, because 1321621661 - 2² = 1321621657 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1321621681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 660810830 + 660810831.

It is an arithmetic number, because the mean of its divisors is an integer number (660810831).

Almost surely, 2^1321621661 is an apocalyptic number.

It is an amenable number.

1321621661 is a deficient number, since it is larger than the sum of its proper divisors (1).

1321621661 is an equidigital number, since it uses as much as digits as its factorization.

1321621661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2592, while the sum is 29.

The square root of 1321621661 is about 36354.1147739840. The cubic root of 1321621661 is about 1097.4103436670.

Adding to 1321621661 its reverse (1661261231), we get a palindrome (2982882892).

The spelling of 1321621661 in words is "one billion, three hundred twenty-one million, six hundred twenty-one thousand, six hundred sixty-one".