|
| |
|
|
A105405
|
|
Numbers k such that prime(k)-1 and prime(k+3)-1 have the same largest prime factor.
|
|
0
|
|
|
|
98, 156, 615, 1474, 2313, 66826, 82099, 150425, 188513, 274638, 321482, 523573, 874881, 6872507, 8101145, 22658038, 95011150, 159081273, 381064119, 509331868, 1216774420, 3067461737, 3356013378, 5447285266, 14949553319, 15007703651, 19495563000, 177439269404, 241783229062
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,1
|
|
|
LINKS
|
|
|
|
MATHEMATICA
|
Do[p = Prime[n] - 1; q = Prime[n+3] - 1; l = Select[Divisors[p], PrimeQ]; m = Select[Divisors[q], PrimeQ]; If[Max[l] == Max[m], Print[n]], {n, 1, 10^7}] (* Ryan Propper, Sep 19 2005 *)
|
|
|
PROG
|
(PARI) \\prime indices such that gd of prime(x)+ k and prime(x+m) + k are equal
divpm1(n, m=3, k=-1) = { 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", ") ) ) }
\\Vector of the prime factors of n
ifactor(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) }
|
|
|
CROSSREFS
|
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
|
|
|
EXTENSIONS
|
|
|
|
STATUS
|
approved
|
| |
|
|
