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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.)