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A120226 Numbers n such that a+n and a*n+1 are prime, case a=4. 4
1, 3, 7, 9, 13, 15, 25, 27, 37, 39, 43, 49, 57, 67, 69, 79, 93, 97, 99, 105, 127, 135, 153, 163, 169, 175, 177, 189, 193, 207, 219, 235, 253, 265, 267, 273, 277, 279, 303, 307, 309, 343, 345, 363, 405, 417, 427, 435, 475, 483, 487, 499, 517, 553, 559, 567, 573 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Prime numbers p such that 4+p and 4*p+1 are prime A106057. Case a=5 A120227.
Except for 3, no terms == 3 or 5 (mod 7). - Robert Israel, Jul 26 2019
LINKS
MAPLE
select(t -> isprime(t+4) and isprime(4*t+1), [seq(i, i=1..1000, 2)]); # Robert Israel, Jul 26 2019
MATHEMATICA
Reap[Do[Do[If[PrimeQ[{n+x, n*x+1}]=={True, True}, Sow[x]], {x, 1, 1000, 2}], {n, 4, 4}]][[2, 1]]
Select[Range[600], AllTrue[{4+#, 4#+1}, PrimeQ]&] (* Harvey P. Dale, Nov 14 2022 *)
CROSSREFS
Sequence in context: A000959 A204085 A230076 * A137310 A118567 A118561
KEYWORD
nonn
AUTHOR
Zak Seidov, Jun 10 2006
STATUS
approved

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Last modified July 13 04:46 EDT 2024. Contains 374267 sequences. (Running on oeis4.)