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.

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

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: A065384 A354217 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