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 A235592 Numbers k such that k*(k+1) - prime(k) is prime. 11
 2, 3, 4, 5, 6, 8, 9, 11, 14, 15, 18, 19, 20, 21, 26, 27, 29, 34, 36, 37, 38, 41, 44, 45, 48, 53, 54, 57, 61, 62, 69, 70, 71, 85, 86, 87, 89, 90, 98, 99, 102, 105, 112, 114, 117, 119, 131, 134, 135, 136, 137, 141, 145, 147, 149, 150, 153, 156, 157, 162, 170, 171, 175, 176, 180, 183, 187, 189, 198, 200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It is known that prime(k) <= k*(k+1) for any positive integer k.  The conjecture in A235613 implies that the sequence has infinitely many terms. Conjecture: This sequence contains infinitely many primes. LINKS Zhi-Wei Sun, Table of n, a(n) for n = 1..10000 EXAMPLE a(1) = 2 since 1*2 - prime(1) = 0 is not prime, but 2*3 - prime(2) = 3 is prime. a(2) = 3 since 3*4 - prime(3) = 7 is prime. a(3) = 4 since 4*5 - prime(4) = 13 is prime. MATHEMATICA n=0; Do[If[PrimeQ[k(k+1)-Prime[k]], n=n+1; Print[n, " ", k]], {k, 1, 200}] CROSSREFS Cf. A000040, A235613, A235614. Sequence in context: A177738 A134030 A226189 * A100054 A101271 A093110 Adjacent sequences:  A235589 A235590 A235591 * A235593 A235594 A235595 KEYWORD nonn AUTHOR Zhi-Wei Sun, Jan 12 2014 STATUS approved

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Last modified October 16 03:37 EDT 2019. Contains 328040 sequences. (Running on oeis4.)