A212955 Least k such that k*30^n-1 and k*30^n+1 are twin primes.

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

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 * A372881 A155415 A155273

Adjacent sequences: A212952 A212953 A212954 * A212956 A212957 A212958

Keyword

nonn

Author

Pierre CAMI, Jun 01 2012

Status

approved