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A327581 a(1) is the smallest prime p such that 6*p^2-1 and 6*p^2+1 are twin primes; for n > 1, a(n) is the smallest prime q > a(n-1) such that 6*q^prime(n)-1 and 6*q^prime(n)+1 are twin primes or 0 if no solution exists. 1
5, 0, 2557, 51137, 52057, 55373, 88867, 95273, 179947, 236653, 993647, 1010467, 1935533, 2031767, 2138803, 2849317, 8031343, 11696563, 11715133, 18125993, 22615493, 26766633, 26801393, 29963077, 39377893, 58282927, 70354657, 98988257, 119772847, 141442493, 145460123 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For prime(2) = 3 there is no solution such that 6*q^3-1 and 6*q^3+1 with q prime are twin primes. Because 7 divides 6*p^3-1 when p == 3, 5, 6 mod 7, 7 divides 6*p^3+1 when p == 1, 2, 4 mod 7. Therefore p can only be 7. But then 6*7^3-1 = 11^2*17 and 6*7^3+1 = 29*71 are not prime numbers, so a(2)=0.

LINKS

Table of n, a(n) for n=1..31.

Pierre CAMI, PFGW Script

PROG

(PARI) findp(n, pmin) = {my(pmin = nextprime(pmin+1), q); forprime(p=pmin, , if (isprime(q=6*p^prime(n)-1) && isprime(q+2), return(p)); ); }

lista(nn) = {my(lasta = 2, newa); print1(findp(1, lasta), ", 0"); for (n=3, nn, newa = findp(n, lasta); print1(", ", newa); lasta = newa; ); } \\ Michel Marcus, Sep 20 2019

CROSSREFS

Sequence in context: A215616 A249737 A129205 * A098173 A180977 A269129

Adjacent sequences:  A327578 A327579 A327580 * A327582 A327583 A327584

KEYWORD

nonn

AUTHOR

Pierre CAMI, Sep 17 2019

STATUS

approved

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Last modified October 26 06:08 EDT 2021. Contains 348257 sequences. (Running on oeis4.)