A087273 Largest prime factor of 3*prime(n) + 1.

7, 5, 2, 11, 17, 5, 13, 29, 7, 11, 47, 7, 31, 13, 71, 5, 89, 23, 101, 107, 11, 17, 5, 67, 73, 19, 31, 23, 41, 17, 191, 197, 103, 19, 7, 227, 59, 7, 251, 13, 269, 17, 41, 29, 37, 23, 317, 67, 31, 43, 7, 359, 181, 29, 193, 79, 101, 37, 13, 211, 17, 11, 461, 467, 47, 17, 71, 23

Offset: 1

Author

Labos Elemer, Sep 18 2003

Keywords

• nonn

Comments

a(n) >= 5 except for n = 3. - Robert Israel, Sep 19 2016

Examples

			n=100: p(100)=541, m = 3*541 + 1 = 1624 = 2*2*2*7*29 so a(100)=29.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A006530.

Programs

Magma

[#f eq 0 select 1 else f[#f][1] where f is Factorization(3*NthPrime(n)+1): n in [1..90]]; // Vincenzo Librandi, Sep 20 2016

Maple

seq(max(numtheory:-factorset(3*ithprime(i)+1)),i=1..100); # Robert Israel, Sep 19 2016

Mathematica

ffi[x_] := Flatten[FactorInteger[x]] ma[x_] := Part[Reverse[ffi[x]], 2] Table[ma[3*Prime[w]+1], {w, 1, 100}]
Table[FactorInteger[3Prime[n]+1][[-1,1]],{n,70}] (* Harvey P. Dale, Apr 10 2012 *)

PARI

a(n) = vecmax(factor(3*prime(n)+1)[,1]); \\ Michel Marcus, Sep 19 2016

Formula

a(n) = A006530(1 + 3*A000040(n)).