1221995781 has 32 divisors (see below), whose sum is σ = 1887146880. Its totient is φ = 780772608.

The previous prime is 1221995777. The next prime is 1221995783. The reversal of 1221995781 is 1875991221.

It is not a de Polignac number, because 1221995781 - 2² = 1221995777 is a prime.

It is a super-2 number, since 2×1221995781² = 2986547377563599922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221995783) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 57805 + ... + 76061.

It is an arithmetic number, because the mean of its divisors is an integer number (58973340).

Almost surely, 2^1221995781 is an apocalyptic number.

It is an amenable number.

1221995781 is a deficient number, since it is larger than the sum of its proper divisors (665151099).

1221995781 is a wasteful number, since it uses less digits than its factorization.

1221995781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18370 (or 18364 counting only the distinct ones).

The product of its digits is 90720, while the sum is 45.

The square root of 1221995781 is about 34957.0562404788. The cubic root of 1221995781 is about 1069.1120770119.

The spelling of 1221995781 in words is "one billion, two hundred twenty-one million, nine hundred ninety-five thousand, seven hundred eighty-one".