A097455 - OEIS

%I #10 Oct 26 2019 18:02:09

%S 1,4,6,8,3,2,6,2,3,2,2,2,21,22,24,1,2,1,4,6,2,1,2,5,2,2,13,4,2,2,1,2,

%T 6,7,50,1,2,2,1,2,3,2,12,2,9,8,1,2,4,23,2,24,2,3,2,11,6,16,1,2,4,1,2,

%U 3,2,6,1,2,3,2,1,24,2,11,20,6,26,1,2,2,10,1,16,2,5,4,9,2,7,8,1,2,1,4,125

%N a(n) = gcd(prime(n)+1, composite(n)).

%H Harvey P. Dale, <a href="/A097455/b097455.txt">Table of n, a(n) for n = 1..1000</a>

%t Module[{nn=100,prs,cmps},prs=Prime[Range[nn]];cmps=Take[Complement[ Range[ Prime[nn]],prs],nn];GCD@@@Thread[{prs+1,cmps}]] (* _Harvey P. Dale_, Sep 05 2013 *)

%o (PARI) primecompgcd(n) = { for(x=1,n, y=gcd(prime(x)+1,composite(x)); print1(y",") ) } \ the n-th composite composite(n) = { local(c,x); c=1; x=0; while(c <= n, x++; if(!isprime(x),c++); ); return(x) }

%Y Cf. A000040, A002808.

%K nonn

%O 1,2

%A _Cino Hilliard_, Aug 23 2004