161666506501 has 2 divisors, whose sum is σ = 161666506502. Its totient is φ = 161666506500.

The previous prime is 161666506493. The next prime is 161666506513. The reversal of 161666506501 is 105605666161.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 137470392900 + 24196113601 = 370770^2 + 155551^2 .

It is a cyclic number.

It is not a de Polignac number, because 161666506501 - 2³ = 161666506493 is a prime.

It is a super-2 number, since 2×161666506501² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161666506301) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80833253250 + 80833253251.

It is an arithmetic number, because the mean of its divisors is an integer number (80833253251).

Almost surely, 2^161666506501 is an apocalyptic number.

It is an amenable number.

161666506501 is a deficient number, since it is larger than the sum of its proper divisors (1).

161666506501 is an equidigital number, since it uses as much as digits as its factorization.

161666506501 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 194400, while the sum is 43.

The spelling of 161666506501 in words is "one hundred sixty-one billion, six hundred sixty-six million, five hundred six thousand, five hundred one".