65661221561 has 4 divisors (see below), whose sum is σ = 70712084772. Its totient is φ = 60610358352.

The previous prime is 65661221557. The next prime is 65661221581. The reversal of 65661221561 is 16512216656.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 25358651536 + 40302570025 = 159244^2 + 200755^2 .

It is a cyclic number.

It is not a de Polignac number, because 65661221561 - 2² = 65661221557 is a prime.

It is a super-2 number, since 2×65661221561² (a number of 22 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (65661221501) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2525431586 + ... + 2525431611.

It is an arithmetic number, because the mean of its divisors is an integer number (17678021193).

Almost surely, 2^65661221561 is an apocalyptic number.

It is an amenable number.

65661221561 is a deficient number, since it is larger than the sum of its proper divisors (5050863211).

65661221561 is a wasteful number, since it uses less digits than its factorization.

65661221561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5050863210.

The product of its digits is 129600, while the sum is 41.

The spelling of 65661221561 in words is "sixty-five billion, six hundred sixty-one million, two hundred twenty-one thousand, five hundred sixty-one".