155121217106021 has 4 divisors (see below), whose sum is σ = 155924953982412. Its totient is φ = 154317480229632.

The previous prime is 155121217105999. The next prime is 155121217106033. The reversal of 155121217106021 is 120601712121551.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 51622946077921 + 103498271028100 = 7184911^2 + 10173410^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-155121217106021 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 (155121217106041) 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, 401868437906 + ... + 401868438291.

It is an arithmetic number, because the mean of its divisors is an integer number (38981238495603).

Almost surely, 2^{155121217106021} is an apocalyptic number.

It is an amenable number.

155121217106021 is a deficient number, since it is larger than the sum of its proper divisors (803736876391).

155121217106021 is an equidigital number, since it uses as much as digits as its factorization.

155121217106021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 803736876390.

The product of its (nonzero) digits is 8400, while the sum is 35.

Adding to 155121217106021 its reverse (120601712121551), we get a palindrome (275722929227572).

The spelling of 155121217106021 in words is "one hundred fifty-five trillion, one hundred twenty-one billion, two hundred seventeen million, one hundred six thousand, twenty-one".