1621721655 has 40 divisors (see below), whose sum is σ = 2985683712. Its totient is φ = 841534272.

The previous prime is 1621721627. The next prime is 1621721659. The reversal of 1621721655 is 5561271261.

1621721655 is a `hidden beast` number, since 1 + 621 + 7 + 21 + 6 + 5 + 5 = 666.

It is not a de Polignac number, because 1621721655 - 2⁵ = 1621721623 is a prime.

It is a super-2 number, since 2×1621721655² = 5259962252591878050, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1621721659) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 39127 + ... + 69096.

Almost surely, 2^1621721655 is an apocalyptic number.

1621721655 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

1621721655 is a deficient number, since it is larger than the sum of its proper divisors (1363962057).

1621721655 is a wasteful number, since it uses less digits than its factorization.

1621721655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108277 (or 108268 counting only the distinct ones).

The product of its digits is 25200, while the sum is 36.

The square root of 1621721655 is about 40270.6053468283. The cubic root of 1621721655 is about 1174.8761976096.

The spelling of 1621721655 in words is "one billion, six hundred twenty-one million, seven hundred twenty-one thousand, six hundred fifty-five".