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 A293621 Numbers n such that (2n)^2 + 1 and (2n+2)^2 + 1 are both primes. 0
 1, 2, 7, 12, 27, 62, 102, 192, 232, 317, 322, 357, 547, 572, 587, 622, 637, 657, 687, 782, 807, 837, 842, 982, 1027, 1042, 1047, 1202, 1227, 1267, 1332, 1417, 1462, 1567, 1652, 1767, 1877, 1887, 2012, 2077, 2087, 2182, 2302, 2307, 2367, 2392, 2397, 2477, 2507 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sierpiński proved that under Schinzel's hypothesis H this sequence is infinite. He gives the 24 terms below 10^3. Sierpiński noted that the only triple of consecutive primes of the form (2n)^2 + 1 are for n = 1 (i.e., 1 and 2 are the only consecutive terms in this sequence), since every triple of consecutive terms contains at least one term which is divisible by 5. Subsequence of A001912. LINKS Wacław Sierpiński, Remarque sur la distribution de nombres premiers, Matematički Vesnik, Vol. 2(17), Issue 31 (1965), pp. 77-78. Eric W. Weisstein, Near-Square Prime. Wikipedia, Schinzel's hypothesis H. EXAMPLE 1 is in the sequence since (2*1)^2 + 1 = 5 and (2*1+2)^2 + 1 = 17 are both primes. MATHEMATICA Select[Range[10^4], AllTrue[{(2#)^2+1, (2#+2)^2+1}, PrimeQ] &] PROG (PARI) isok(n) = isprime((2*n)^2 + 1) && isprime((2*n+2)^2 + 1); \\ Michel Marcus, Oct 13 2017 CROSSREFS Cf. A001912, A002496, A002522, A005574, A053755. Sequence in context: A242201 A177747 A288888 * A175879 A102371 A007230 Adjacent sequences:  A293618 A293619 A293620 * A293622 A293623 A293624 KEYWORD nonn AUTHOR Amiram Eldar, Oct 13 2017 STATUS approved

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Last modified May 19 10:36 EDT 2019. Contains 323390 sequences. (Running on oeis4.)