1221265161 has 8 divisors (see below), whose sum is σ = 1809281760. Its totient is φ = 814176756.

The previous prime is 1221265141. The next prime is 1221265217. The reversal of 1221265161 is 1615621221.

1221265161 is a `hidden beast` number, since 1 + 2 + 2 + 1 + 2 + 651 + 6 + 1 = 666.

It is not a de Polignac number, because 1221265161 - 2¹³ = 1221256969 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 45232043 = 1221265161 / (1 + 2 + 2 + 1 + 2 + 6 + 5 + 1 + 6 + 1).

It is not an unprimeable number, because it can be changed into a prime (1221265121) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 22615995 + ... + 22616048.

It is an arithmetic number, because the mean of its divisors is an integer number (226160220).

Almost surely, 2^1221265161 is an apocalyptic number.

It is an amenable number.

1221265161 is a deficient number, since it is larger than the sum of its proper divisors (588016599).

1221265161 is an equidigital number, since it uses as much as digits as its factorization.

1221265161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45232052 (or 45232046 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 1221265161 is about 34946.6044273260. The cubic root of 1221265161 is about 1068.8989637854.

Adding to 1221265161 its reverse (1615621221), we get a palindrome (2836886382).

The spelling of 1221265161 in words is "one billion, two hundred twenty-one million, two hundred sixty-five thousand, one hundred sixty-one".