1221645697381 has 4 divisors (see below), whose sum is σ = 1221674018764. Its totient is φ = 1221617376000.

The previous prime is 1221645697369. The next prime is 1221645697403. The reversal of 1221645697381 is 1837965461221.

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 412923193281 + 808722504100 = 642591^2 + 899290^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221645697381 - 2³¹ = 1219498213733 is a prime.

It is a super-2 number, since 2×1221645697381² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221645697331) 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, 14095890 + ... + 14182291.

It is an arithmetic number, because the mean of its divisors is an integer number (305418504691).

Almost surely, 2^{1221645697381} is an apocalyptic number.

It is an amenable number.

1221645697381 is a deficient number, since it is larger than the sum of its proper divisors (28321383).

1221645697381 is an equidigital number, since it uses as much as digits as its factorization.

1221645697381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28321382.

The product of its digits is 4354560, while the sum is 55.

The spelling of 1221645697381 in words is "one trillion, two hundred twenty-one billion, six hundred forty-five million, six hundred ninety-seven thousand, three hundred eighty-one".