A125674 For any number larger than 2, the primes reached when you start with n and concatenate the sum of its prime factors with its largest prime factor, then repeat the process until you eventually reach a prime, or print a -1 if you never do.

1, 2, 3, 127, 5, 53, 7, 3331, 137, 888691, 11, 73, 13, 97, -1, -1, 17, 83, 19, 489479, 107, 4523, 23, 12073, 157, 519509, 12073, 1913, 29, 157, 31, -1, 33643361, 448257236701, 127, 103, 37, 27023222702059, 1613, -1, 41, 127, 43, 1511, -1, -1, 47, 113, -1, 3631, 2017, 17401297, 53, 113, -1, 137, 511439, -1, 59

Offset

1,2

References

J. Earls & J. Rogers, "I Sin Every Number", IF(Sid_Vicious == TRUE && Alan_Turing == TRUE){ERROR_Cyberpunk();}, Lulu Press, NY, 2007, p. 126.

Links

Table of n, a(n) for n=1..59.

Amazon.com, IF(Sid_Vicious == TRUE && Alan_Turing == TRUE){ERROR_Cyberpunk();}(Title of book).

Example

Start with 4. Its factors are 2 and 2. Sum them to get 4 and then concatenate that to its largest prime factor to get 42. It is not a prime. The factors of 42 are: 2, 3, 7. Sum them to get 12 and concatenate it with its largest prime factor to get 127. That number is prime. So a(4) = 127.

Crossrefs

Cf. A037274.

Sequence in context: A371271 A334661 A258968 * A180533 A095841 A004865

Adjacent sequences: A125671 A125672 A125673 * A125675 A125676 A125677

Keyword

sign,base

Author

Jason Earls, Jan 30 2007

Status

approved