(30b) Perrin Sequence & a Quick Prime Test - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: HP Software Libraries (/forum-10.html) +--- Forum: General Software Library (/forum-13.html) +--- Thread: (30b) Perrin Sequence & a Quick Prime Test (/thread-2456.html) (30b) Perrin Sequence & a Quick Prime Test - Gerald H - 11-20-2014 04:44 PM Perrin sequence for integer input > 0 0 P0 1 Lbl 01 2 STO 2 3 3 4 STO 1 5 1 6 +/- 7 = 8 1 9 = 10 1 11 +/- 12 = 13 Lbl 00 14 RCL 1 15 R↓ 16 + 17 STO 1 18 R↓ 19 Swap 20 1 21 STO- 2 22 RCL* 2 23 GT 00 24 RCL 1 25 RTN The Perrin sequence beginning at index 1 is 0, 2, 3, 2, 5, 5, 7, 10, 12, 17, 22, 29, 39, 51, 68, 90, 119, 158, 209, 277, 367, 486 … The programme returns exact values for indices 1 to 98, thereafter approximate. A pleasant attribute of the series is that if the index divides the indexed value with non-zero remainder the index is not prime. Accordingly, a quick prime test follows: 0 P1 1 STO 3 2 Call01 3 RCL/ 3 4 Math 5 Up 6 Input 7 0 8 ?= 9 RTN All primes in the range 2 to 98 are correctly identified with a 1 returned, as are all non-primes shown by a 0.