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a(n) is the n-th prime == 1 (mod n).
5

%I #19 Nov 13 2020 18:07:09

%S 2,5,19,29,71,43,211,193,271,191,661,277,937,463,691,769,1531,613,

%T 2357,1021,1723,1409,3313,1609,3701,2029,3187,2437,6961,1741,7193,

%U 3617,4951,3877,7001,3169,10657,6271,7879,5521,13613,3823,15137,7349,9091,7499

%N a(n) is the n-th prime == 1 (mod n).

%C a(n) is the n-th prime in the arithmetic progression with first term 1 and common difference n.

%C Main diagonal of A077316.

%H Zak Seidov, <a href="/A077317/b077317.txt">Table of n, a(n) for n = 1..1000</a>

%e a(5) = 71, the fifth prime in the sequence 1, 6, 11, 16, 21, 26, 31, 36, 41, 46, 51, 56, 61, 66, 71, ...

%p a:=proc(n) local N, B, j: N:=[seq(n*x+1,x=0..500)]: B:={}: for j from 1 to nops(N) do if isprime(N[j])=true then B:=B union {N[j]} else fi od: B[n]: end: seq(a(n),n=1..55); # _Emeric Deutsch_, Sep 03 2005

%t Module[{nn=50,prs=Prime[Range[3000]]},Join[{2},Table[Select[prs,Mod[#,n] == 1&][[n]],{n,2,nn}]]] (* _Harvey P. Dale_, Nov 13 2020 *)

%Y Cf. A034694, A077316, A077318, A077319, A093871.

%K nonn

%O 1,1

%A _Amarnath Murthy_, Nov 04 2002, Jul 23 2005 (submitted incorrectly on two separate occasions; each time it has had to be corrected)

%E Edited, corrected and extended by _Emeric Deutsch_, Sep 03 2005 and by _Franklin T. Adams-Watters_, Aug 29 2006

%E Edited by _N. J. A. Sloane_, Aug 23 2008 at the suggestion of _R. J. Mathar_