A105408 - OEIS

%I #8 Oct 01 2013 17:58:10

%S 1,3,5,16,64,85,266,547,1709,1771,4415,9545,13129,24130,34201,213122,

%T 396981,543586,555301,609182,1040051,1870869,2547634,3052012,5076662,

%U 8530768,9773479,18563382,26505870,89046072,169660944,193691856,200228233,359241899,597825925,914450195,1020520062,1585841242,1970793485

%N Indices n of primes p(n), p(n+4) such that p(n)+1 and p(n+4)+1 have the same largest prime factor.

%e p(1)+1=3 and p(5)+1=12 have the same largest prime factor.

%o (PARI) \prime indices such that gd of prime(x)+ k and prime(x+m) + k are equal divpm1(n,m,k) = { local(x,l1,l2,v1,v2); for(x=2,n, v1 = ifactor(prime(x)+ k); v2 = ifactor(prime(x+m)+k); l1 = length(v1); l2 = length(v2); if(v1[l1] == v2[l2], print1(x",") ) ) } ifactor(n) = \Vector of the prime factors of n { local(f,j,k,flist); flist=[]; f=Vec(factor(n)); for(j=1,length(f[1]), for(k = 1,f[2][j],flist = concat(flist,f[1][j]) ); ); return(flist) }

%K nonn

%O 2,2

%A _Cino Hilliard_, May 01 2005

%E More terms from _Erich Friedman_, Aug 26 2005

%E Corrected and extended by _Donovan Johnson_, Apr 03 2008