1216631021 has 4 divisors (see below), whose sum is σ = 1216702944. Its totient is φ = 1216559100.

The previous prime is 1216630969. The next prime is 1216631029. The reversal of 1216631021 is 1201366121.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1201366121 = 43 ⋅27938747.

It is a cyclic number.

It is not a de Polignac number, because 1216631021 - 2¹⁸ = 1216368877 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1216631029) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4856 + ... + 49566.

It is an arithmetic number, because the mean of its divisors is an integer number (304175736).

Almost surely, 2^1216631021 is an apocalyptic number.

It is an amenable number.

1216631021 is a deficient number, since it is larger than the sum of its proper divisors (71923).

1216631021 is an equidigital number, since it uses as much as digits as its factorization.

1216631021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71922.

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 1216631021 is about 34880.2382589340. The cubic root of 1216631021 is about 1067.5452566706.

Adding to 1216631021 its reverse (1201366121), we get a palindrome (2417997142).

The spelling of 1216631021 in words is "one billion, two hundred sixteen million, six hundred thirty-one thousand, twenty-one".