121661561 has 6 divisors (see below), whose sum is σ = 141524730. Its totient is φ = 104281296.

The previous prime is 121661531. The next prime is 121661569. The reversal of 121661561 is 165166121.

It can be written as a sum of positive squares in only one way, i.e., 98803600 + 22857961 = 9940^2 + 4781^2 .

It is not a de Polignac number, because 121661561 - 2²⁶ = 54552697 is a prime.

It is a super-3 number, since 3×121661561³ (a number of 25 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (121661569) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1241396 + ... + 1241493.

It is an arithmetic number, because the mean of its divisors is an integer number (23587455).

Almost surely, 2^121661561 is an apocalyptic number.

It is an amenable number.

121661561 is a deficient number, since it is larger than the sum of its proper divisors (19863169).

121661561 is an equidigital number, since it uses as much as digits as its factorization.

121661561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2482903 (or 2482896 counting only the distinct ones).

The product of its digits is 2160, while the sum is 29.

The square root of 121661561 is about 11030.0299636946. The cubic root of 121661561 is about 495.5085220629.

The spelling of 121661561 in words is "one hundred twenty-one million, six hundred sixty-one thousand, five hundred sixty-one".