A329920 Smallest k such that 6*k*A121940(n)-1 and 6*k*A121940(n)+1 are twin primes.

1, 2, 2, 15, 36, 10, 13, 26, 30, 228, 24, 138, 520, 59, 110, 456, 700, 670, 146, 300, 390, 53, 2335, 340, 159, 340, 65, 475, 785, 1145, 759, 3557, 490, 169, 990, 1527, 704, 3379, 1426, 1927, 2397, 600, 1603, 4809, 9815, 58, 35, 364, 361, 123, 2197, 4054, 1867, 1827, 5048

Offset

1,2

Links

Table of n, a(n) for n=1..55.

Example

A121940(1)=7, 6*1*7-1=41, 41 and 43 are twin primes so a(1)=1.
A121940(2)=91, 6*2*91-1=1091, 1091 and 1093 are twin primes so a(2)=2.

Prog

(PFGW Script)
SCRIPT
DIM i, 0
DIM j
DIM k, 0
DIM n, 1
OPENFILEOUT myf, a(n).txt
OPENFILEIN maf, a002476.txt
LABEL a
SET i, i+1
IF i>100 THEN END
GETNEXT j, maf
SET n, n*j
SET k, 0
LABEL b
SET k, k+1
PRP k*6*n+1, k
IF ISPRP THEN GOTO c
GOTO b
LABEL c
PRP k*6*n-1, k
IF ISPRP THEN GOTO d
GOTO b
LABEL d
WRITE myf, k
GOTO a
(PARI) lista(nn) = {my(pp = 1); forprime (p = 1, nn, if (Mod(p, 6) == +1, pp *= p; my(k=1); while (!isprime(6*k*pp-1) || !isprime(6*k*pp+1), k++); print1(k, ", "); ); ); } \\ Michel Marcus, Nov 25 2019

Crossrefs

Cf. A001359, A002476, A006512, A121940, A173937, A329336, A329916.

Sequence in context: A365086 A185044 A185244 * A006929 A216613 A215900

Adjacent sequences: A329917 A329918 A329919 * A329921 A329922 A329923

Keyword

nonn

Author

Pierre CAMI, Nov 24 2019

Status

approved