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 A139221 Numbers k such that both 41+(k+k^2)/2 and 41+(k+k^2) are primes. 3
 0, 3, 11, 20, 23, 27, 32, 39, 48, 51, 59, 60, 83, 108, 111, 116, 128, 132, 135, 171, 188, 203, 212, 227, 240, 263, 275, 315, 324, 356, 359, 363, 384, 392, 447, 476, 479, 515, 528, 588, 627, 647, 648, 672, 731, 759, 780, 804, 839, 864, 875, 900, 903, 968, 975 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Intersection of A139220 and A056561. LINKS Daniel Starodubtsev, Table of n, a(n) for n = 1..10000 EXAMPLE If k = 11 then 41 + (k + k^2) / 2 = 107 (prime) and 41 + (k + k^2) = 173 (prime). MATHEMATICA Select[Table[Range[0, 2000]], PrimeQ[41+(#+#^2)/2]&&PrimeQ[41+#+#^2]&] PROG (Magma) [k:k in [0..1000]| IsPrime(41+(k+k^2) div 2) and IsPrime(41+k+k^2)]; // Marius A. Burtea, Feb 12 2020 (PARI) for(n=0, 1000, if(isprime(binomial(n+1, 2) +41) && isprime(n^2+n+41), print1(n", "))) \\ G. C. Greubel, Feb 12 2020 (Sage) [n for n in (0..1000) if is_prime(binomial(n+1, 2)+41) and is_prime(n^2+n+41)] # G. C. Greubel, Feb 12 2020 CROSSREFS Cf. A000217, A056561, A139219, A139220. Sequence in context: A279257 A166096 A139220 * A300381 A006876 A031239 Adjacent sequences: A139218 A139219 A139220 * A139222 A139223 A139224 KEYWORD nonn AUTHOR Zak Seidov, Apr 11 2008 STATUS approved

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Last modified March 23 15:31 EDT 2023. Contains 361445 sequences. (Running on oeis4.)