1620505661 has 2 divisors, whose sum is σ = 1620505662. Its totient is φ = 1620505660.

The previous prime is 1620505657. The next prime is 1620505699. The reversal of 1620505661 is 1665050261.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1600480036 + 20025625 = 40006^2 + 4475^2 .

It is a cyclic number.

It is not a de Polignac number, because 1620505661 - 2² = 1620505657 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1620505651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810252830 + 810252831.

It is an arithmetic number, because the mean of its divisors is an integer number (810252831).

Almost surely, 2^1620505661 is an apocalyptic number.

It is an amenable number.

1620505661 is a deficient number, since it is larger than the sum of its proper divisors (1).

1620505661 is an equidigital number, since it uses as much as digits as its factorization.

1620505661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10800, while the sum is 32.

The square root of 1620505661 is about 40255.5047291672. The cubic root of 1620505661 is about 1174.5824769157.

The spelling of 1620505661 in words is "one billion, six hundred twenty million, five hundred five thousand, six hundred sixty-one".