A108939 Triangle read by rows in which row n lists all primes p such that p-1|n.
2, 2, 3, 2, 2, 3, 5, 2, 2, 3, 7, 2, 2, 3, 5, 2, 2, 3, 11, 2, 2, 3, 5, 7, 13, 2, 2, 3, 2, 2, 3, 5, 17, 2, 2, 3, 7, 19, 2, 2, 3, 5, 11, 2, 2, 3, 23, 2, 2, 3, 5, 7, 13, 2, 2, 3, 2, 2, 3, 5, 29, 2, 2, 3, 7, 11, 31, 2, 2, 3, 5, 17, 2, 2, 3, 2, 2, 3, 5, 7, 13, 19, 37, 2, 2, 3, 2, 2, 3, 5, 11, 41, 2
Offset: 1
Examples
Row n = 1 : 2 because 1|1. Row n = 2 : 2, 3 because 1|2 and 2|2. Row n = 3 : 2 because 1|3. Row n = 4 : 2, 3, 5 because 1|4, 2|4 and 4|4. Row n = 5 : 2 because 1|5. Row n = 6 : 2, 3, 7 because 1|6, 2|6 and 6|6. Row n = 7 : 2 because 1|7. Row n = 8 : 2, 3, 5 because 1|8, 2|8 and 4|8. Row n = 9 : 2 because 1|9. Row n = 10 : 2, 3, 11 because 1|10, 2|10 and 10|10. Row n = 11 : 2 because 1|11. Row n = 12 : 2, 3, 5, 7, 13 because 1|12, 2|12, 4|12, 6|12 = and 12|12.
Links
- Robert Israel, Table of n, a(n) for n = 1..10000 (rows 1 to 3261, flattened)
Programs
-
Maple
with(numtheory): for n from 1 to 20 do div:=divisors(n): A:=[seq(div[j]+1,j=1..tau(n))]: B:={}: for i from 1 to tau(n) do if isprime(A[i])=true then B:=B union {A[i]} else B:=B: fi: od: C:=convert(B,list): b[n]:=C: od: for n from 1 to 20 do b[n]:=b[n] od; # yields sequence in triangular form - Emeric Deutsch, Aug 03 2005
Extensions
Corrected by Robert Israel, Sep 21 2023
Comments