1213921981 has 2 divisors, whose sum is σ = 1213921982. Its totient is φ = 1213921980.

The previous prime is 1213921957. The next prime is 1213921987. The reversal of 1213921981 is 1891293121.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 618317956 + 595604025 = 24866^2 + 24405^2 .

It is a cyclic number.

It is not a de Polignac number, because 1213921981 - 2¹¹ = 1213919933 is a prime.

It is a super-2 number, since 2×1213921981² = 2947213151909928722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 1213921981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1213921987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 606960990 + 606960991.

It is an arithmetic number, because the mean of its divisors is an integer number (606960991).

Almost surely, 2^1213921981 is an apocalyptic number.

It is an amenable number.

1213921981 is a deficient number, since it is larger than the sum of its proper divisors (1).

1213921981 is an equidigital number, since it uses as much as digits as its factorization.

1213921981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7776, while the sum is 37.

The square root of 1213921981 is about 34841.3831671477. The cubic root of 1213921981 is about 1066.7523096057.

The spelling of 1213921981 in words is "one billion, two hundred thirteen million, nine hundred twenty-one thousand, nine hundred eighty-one".