1216561621 has 8 divisors (see below), whose sum is σ = 1397008800. Its totient is φ = 1047756240.

The previous prime is 1216561603. The next prime is 1216561631. The reversal of 1216561621 is 1261656121.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1216561621 - 2¹⁵ = 1216528853 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1216561631) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2910226 + ... + 2910643.

It is an arithmetic number, because the mean of its divisors is an integer number (174626100).

Almost surely, 2^1216561621 is an apocalyptic number.

1216561621 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1216561621 is a deficient number, since it is larger than the sum of its proper divisors (180447179).

1216561621 is a wasteful number, since it uses less digits than its factorization.

1216561621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5820899.

The product of its digits is 4320, while the sum is 31.

The square root of 1216561621 is about 34879.2434120925. The cubic root of 1216561621 is about 1067.5249577062.

The spelling of 1216561621 in words is "one billion, two hundred sixteen million, five hundred sixty-one thousand, six hundred twenty-one".