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 A212955 Least k such that k*30^n-1 and k*30^n+1 are twin primes. 2
 1, 7, 19, 44, 52, 19, 8, 77, 82, 40, 14, 140, 44, 119, 592, 217, 272, 744, 737, 536, 1298, 219, 839, 977, 226, 773, 576, 1111, 461, 130, 104, 1152, 2083, 721, 587, 6312, 2126, 489, 331, 6008, 4582, 420, 14, 3951, 432, 2703, 4498, 2219, 1029, 1411, 2392, 3431 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Pierre CAMI, Table of n, a(n) for n = 1..270 EXAMPLE 1*30^1-1 = 29 is prime and 1*30^1+1 = 31 is prime. Hence a(1) = 1. MATHEMATICA Table[k = 1; While[! PrimeQ[k*30^n + 1] || ! PrimeQ[k*30^n - 1], k++]; k, {n, 60}] (* T. D. Noe, Jun 01 2012 *) tpk[n_]:=Module[{k=1, c=30^n}, While[!AllTrue[k*c+{1, -1}, PrimeQ], k++]; k]; Array[tpk, 60] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Mar 26 2015 *) PROG PFGW64 and SCRIPTIFY from Primeform Group command : pfgw64 -f in.txt in.txt file : SCRIPT DIM nn, 0 DIM kk, 0 DIMS tt OPENFILEOUT myfile, a(n).txt LABEL loopn SET nn, nn+1 IF nn>270 THEN END SET kk, 0 LABEL loopk SET kk, kk+1 SETS tt, %d, %d\,; nn; kk PRP kk*30^nn-1, tt IF ISPRP THEN GOTO a IF ISPRIME THEN GOTO a GOTO loopk LABEL a PRP kk*30^nn+1, tt IF ISPRP THEN GOTO b IF ISPRIME THEN GOTO b GOTO loopk LABEL b WRITE myfile, tt GOTO loopn CROSSREFS Sequence in context: A155399 A330854 A268926 * A155415 A155273 A277613 Adjacent sequences:  A212952 A212953 A212954 * A212956 A212957 A212958 KEYWORD nonn AUTHOR Pierre CAMI, Jun 01 2012 STATUS approved

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Last modified June 18 13:21 EDT 2021. Contains 345112 sequences. (Running on oeis4.)