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 A213881 k such that 10^(2*k+1)-j*10^k-1 is prime for some j = 1, 2, 4, 5, 7 or 8. 0
 1, 5, 8, 9, 13, 14, 22, 26, 36, 43, 88, 104, 112, 118, 169, 181, 198, 352, 378, 530, 622, 697, 1136, 1246, 1315, 1579, 1798, 1918, 2874, 2917, 4228, 5876, 6768, 10052, 17864, 18077, 22652, 23034, 25448, 47509, 52140, 55862, 62938, 67404, 134739, 145126 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The j values are either 7 and 8 for k=1. For larger k, there is one j only: 8, 7, 7, 8, 5, 5, 1, 5, 8, 4, 5, 4, 2, 8, 8, 4, 7, 1, 7, 4, 7, 5, 1, 7, 8, 1, 7, 7, 1, 4, 7, 7, 4, 5, 8, 8, 1, 5, 1, 1, 4, 7, 1, 7, 2. The next k is probably near 160000 to 200000 LINKS Chris Caldwell, Palindrome Chris Caldwell, Daren Bedwell EXAMPLE 10^3-7*10^1-1=929 prime as 10^3-8*10^1-1=919 so a(1)=1. PROG PFGW64 and SCRIPTIFY from Primeform Group Command : pfgw64 -f in.txt in.txt file : SCRIPT DIM nn, 0 DIM kk DIMS tt OPENFILEOUT myfile, a(n).txt LABEL loopn SET nn, nn+1 IF nn>200000 THEN END SET kk, 0 LABEL loopk SET kk, kk+1 IF kk%3==0 THEN SET kk, kk+1 IF kk>8 THEN GOTO loopn SETS tt, %d, %d\,; nn; kk PRP (10^(nn+1)-kk)*10^nn-1, tt IF ISPRIME THEN GOTO a IF ISPRP THEN GOTO a GOTO loopk LABEL a WRITE myfile, tt GOTO loopk Results in a(n) CROSSREFS Cf. A115073, A183187 Sequence in context: A314575 A286454 A293913 * A179832 A334919 A047616 Adjacent sequences:  A213878 A213879 A213880 * A213882 A213883 A213884 KEYWORD nonn,base AUTHOR Pierre CAMI, Jun 23 2012 STATUS approved

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Last modified May 22 13:12 EDT 2022. Contains 353950 sequences. (Running on oeis4.)