1621155651961 has 2 divisors, whose sum is σ = 1621155651962. Its totient is φ = 1621155651960.

The previous prime is 1621155651949. The next prime is 1621155652031. The reversal of 1621155651961 is 1691565511261.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1531369125225 + 89786526736 = 1237485^2 + 299644^2 .

It is a cyclic number.

It is not a de Polignac number, because 1621155651961 - 2¹¹ = 1621155649913 is a prime.

It is not a weakly prime, because it can be changed into another prime (1621155651931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810577825980 + 810577825981.

It is an arithmetic number, because the mean of its divisors is an integer number (810577825981).

Almost surely, 2^{1621155651961} is an apocalyptic number.

It is an amenable number.

1621155651961 is a deficient number, since it is larger than the sum of its proper divisors (1).

1621155651961 is an equidigital number, since it uses as much as digits as its factorization.

1621155651961 is an evil number, because the sum of its binary digits is even.

The product of its digits is 486000, while the sum is 49.

The spelling of 1621155651961 in words is "one trillion, six hundred twenty-one billion, one hundred fifty-five million, six hundred fifty-one thousand, nine hundred sixty-one".