A209255 - OEIS

A209255

Integers n such that (prime(n)*prime(n+1)+1)/2 is prime.

91, 327, 404, 653, 802, 804, 885, 999, 1003, 1045, 1208, 1362, 1365, 1452, 1461, 1541, 1551, 1717, 1738, 1759, 1820, 1877, 1883, 1908, 1939, 1943, 2064, 2135, 2146, 2155, 2214, 2313, 2316, 2325, 2498, 2507, 2508, 2555, 2613, 2623, 2686, 2736, 2750, 2905

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Corresponding primes: 111847, 2400169, 3872527, 11921827, 18954307, 19127041, 23646547, 31307767, 31545607, 3478606, 47990587, 63472627, 63765907, 73580509, 74823127, 83812387, 84773149, 107501767, 11006826, 113507227, 121882867, 130136827, 131300941, 135548041, 141103129, 141742267.

LINKS

Ray Chandler, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) = 91 because prime(91) = 467, prime(92) = 479 and (467*479+1)/2 = 111847 (prime).

MATHEMATICA

Select[Range[2000], PrimeQ[(Prime[#]*Prime[# + 1] + 1)/2] &] (* G. C. Greubel, Jan 05 2018 *)

Position[Partition[Prime[Range[3000]], 2, 1], _?(PrimeQ[(#[[1]]#[[2]]+1)/2]&), 1, Heads->False]//Flatten (* Harvey P. Dale, Jun 30 2022 *)

PROG

(PARI) for(n=2, 2000, if(isprime((prime(n)*prime(n+1)+1)/2), print1(n", ")))

CROSSREFS

Sequence in context: A224460 A350206 A020441 * A273799 A063137 A234131

Adjacent sequences: A209252 A209253 A209254 * A209256 A209257 A209258

KEYWORD

nonn

AUTHOR

Zak Seidov, Jan 14 2013

STATUS

approved