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 A340339 a(n) is the least prime p such that n*p+b is prime, where b=1 if n is even or 2 if n is odd, and p > a(n-1) if n >= 2. 2
 3, 5, 7, 13, 19, 23, 47, 71, 73, 97, 109, 139, 173, 239, 241, 271, 283, 307, 353, 443, 449, 499, 547, 563, 593, 647, 683, 709, 739, 743, 761, 809, 839, 859, 877, 907, 941, 971, 991, 1009, 1021, 1049, 1103, 1217, 1237, 1291, 1297, 1319, 1499, 1559, 1619, 1663, 1747, 1777, 1811, 1997, 2053, 2161 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA A340340(n) = n*a(n)+A000034(n). EXAMPLE a(4) = 13 because 13 is the least prime p > 7 such that 4*p+1 is prime. MAPLE f:= proc(n, p0)     local p, a, v;     if n::odd then a:= 2 else a:= 1 fi;     p:= p0;     do p:= nextprime(p)     until isprime(n*p+a);     return p end proc: p:= 2: R:= NULL: for n from 1 to 100 do   p:= f(n, p);   R:= R, p; od: R; CROSSREFS Cf. A000034, A340340. Sequence in context: A155189 A065384 A338567 * A126108 A100859 A336369 Adjacent sequences:  A340336 A340337 A340338 * A340340 A340341 A340342 KEYWORD nonn AUTHOR J. M. Bergot and Robert Israel, Jan 04 2021 STATUS approved

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Last modified June 17 17:39 EDT 2021. Contains 345085 sequences. (Running on oeis4.)