A340741 Numbers k such that A340740(k) is prime.
7, 8, 9, 11, 12, 13, 15, 18, 19, 28, 31, 32, 34, 36, 44, 46, 47, 51, 52, 62, 64, 67, 69, 70, 73, 83, 88, 109, 110, 112, 128, 148, 153, 159, 189, 190, 192, 206, 212, 214, 222, 224, 226, 244, 245, 261, 267, 269, 280, 282, 283, 287, 300, 305, 312, 315, 319, 323, 366, 370, 378, 381, 388, 394, 404
Offset: 1
Keywords
Examples
a(3) = 9 is a term because A340740(9) = 2 is prime.
Links
- Robert Israel, Table of n, a(n) for n = 1..5000
Programs
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Maple
f:= proc(n) local k; add(`if`(igcd(k,n)=1, n mod k, 0),k=1..floor(n/2)) end proc: select(t -> isprime(f(t)), [$1..1000]);
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Mathematica
A340741[n_] := Position[Table[ PrimeQ[Sum[ Mod[m, i]*Floor[1/GCD[i, m]], {i, Floor[(m - 1)/2]}]], {m, 1, n}], True] // Flatten; A340741[404] (* Robert P. P. McKone, Jan 19 2021 *)
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PARI
isok(n) = isprime(sum(k=1, n\2, if (gcd(k, n)==1, n%k))); \\ Michel Marcus, Jan 18 2021