1221617778 has 16 divisors (see below), whose sum is σ = 2444223936. Its totient is φ = 407041200.

The previous prime is 1221617759. The next prime is 1221617783. The reversal of 1221617778 is 8777161221.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 24601 + ... + 55212.

It is an arithmetic number, because the mean of its divisors is an integer number (152763996).

Almost surely, 2^1221617778 is an apocalyptic number.

1221617778 is an abundant number, since it is smaller than the sum of its proper divisors (1222606158).

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

1221617778 is a wasteful number, since it uses less digits than its factorization.

1221617778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82369.

The product of its digits is 65856, while the sum is 42.

The square root of 1221617778 is about 34951.6491456412. The cubic root of 1221617778 is about 1069.0018286090.

Adding to 1221617778 its reverse (8777161221), we get a palindrome (9998778999).

The spelling of 1221617778 in words is "one billion, two hundred twenty-one million, six hundred seventeen thousand, seven hundred seventy-eight".