1221721776 has 60 divisors (see below), whose sum is σ = 3729958440. Its totient is φ = 370218240.

The previous prime is 1221721763. The next prime is 1221721777. The reversal of 1221721776 is 6771271221.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 1221721776.

It is not an unprimeable number, because it can be changed into a prime (1221721777) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 384061 + ... + 387228.

It is an arithmetic number, because the mean of its divisors is an integer number (62165974).

Almost surely, 2^1221721776 is an apocalyptic number.

1221721776 is a gapful number since it is divisible by the number (16) formed by its first and last digit.

It is an amenable number.

1221721776 is an abundant number, since it is smaller than the sum of its proper divisors (2508236664).

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

1221721776 is a wasteful number, since it uses less digits than its factorization.

1221721776 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 771314 (or 771305 counting only the distinct ones).

The product of its digits is 16464, while the sum is 36.

The square root of 1221721776 is about 34953.1368549376. The cubic root of 1221721776 is about 1069.0321629464.

Adding to 1221721776 its reverse (6771271221), we get a palindrome (7992992997).

The spelling of 1221721776 in words is "one billion, two hundred twenty-one million, seven hundred twenty-one thousand, seven hundred seventy-six".