1221356565 has 48 divisors (see below), whose sum is σ = 2487139200. Its totient is φ = 546618240.

The previous prime is 1221356531. The next prime is 1221356573. The reversal of 1221356565 is 5656531221.

1221356565 is a `hidden beast` number, since 1 + 22 + 13 + 565 + 65 = 666.

It is not a de Polignac number, because 1221356565 - 2¹⁸ = 1221094421 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 88465 + ... + 101334.

It is an arithmetic number, because the mean of its divisors is an integer number (51815400).

Almost surely, 2^1221356565 is an apocalyptic number.

1221356565 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

1221356565 is an abundant number, since it is smaller than the sum of its proper divisors (1265782635).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1221356565 is a wasteful number, since it uses less digits than its factorization.

1221356565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 189834 (or 189831 counting only the distinct ones).

The product of its digits is 54000, while the sum is 36.

The square root of 1221356565 is about 34947.9121693986. The cubic root of 1221356565 is about 1068.9256299036.

Adding to 1221356565 its reverse (5656531221), we get a palindrome (6877887786).

The spelling of 1221356565 in words is "one billion, two hundred twenty-one million, three hundred fifty-six thousand, five hundred sixty-five".