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 A128780 Numbers n such that n^k+(n+1)^k is prime for k = 1, 2, 4. 4
 1, 2, 9, 14, 189, 204, 230, 320, 680, 765, 1080, 1190, 1359, 1364, 1500, 1764, 1850, 2049, 2115, 2360, 2379, 2919, 3050, 3110, 3179, 3579, 3794, 4164, 4215, 4470, 5355, 5619, 5630, 5664, 5810, 5889, 5979, 6035, 6150, 6269, 6824, 6960, 7275, 8045, 8259 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS n^k+(n+1)^k is prime only for k = power of 2. There are 1242 terms < 10^6. All terms > 2 are congruent to 0 or 4 (mod 5). - Robert Israel, Mar 29 2017 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE {2+1, 2^2+3^2,2^4+3^4} = {3,13,97} all prime, {9+10, 9^2+10^2,9^4+10^4} = {19,181,16561} all prime. MAPLE select(n -> isprime(2*n+1) and isprime(2*n^2+2*n+1) and isprime(n^4+(n+1)^4), [1, 2, seq(seq(5*i+j, j=[0, 4]), i=1..10000)]); # Robert Israel, Mar 29 2017 MATHEMATICA pnQ[n_]:=And@@PrimeQ/@(n^{1, 2, 4}+(n+1)^{1, 2, 4}); Select[Range[9000], pnQ]  (* Harvey P. Dale, Apr 06 2011 *) CROSSREFS Subset of A068501. Sequence in context: A024470 A024472 A279089 * A178849 A217367 A076208 Adjacent sequences:  A128777 A128778 A128779 * A128781 A128782 A128783 KEYWORD nonn AUTHOR Zak Seidov, Mar 28 2007 STATUS approved

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Last modified September 23 20:42 EDT 2021. Contains 347617 sequences. (Running on oeis4.)