

A071407


Least k such that k*prime(n) + 1 and k*prime(n)  1 are twin primes.


5



2, 2, 6, 6, 18, 24, 6, 12, 6, 12, 42, 54, 30, 24, 6, 120, 18, 258, 24, 18, 84, 132, 54, 48, 114, 42, 6, 6, 48, 24, 144, 30, 6, 12, 12, 78, 24, 36, 30, 54, 132, 18, 90, 36, 66, 18, 42, 30, 120, 30, 36, 42, 18, 18, 54, 84, 60, 12, 210, 12, 6, 60, 150, 102, 6, 210, 30, 24, 6
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


COMMENTS

Note that 6 divides a(n) for n > 2.  T. D. Noe, Jan 07 2013


LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000


EXAMPLE

n=4: prime(4)=7, a(4)=6 because 6*prime(4)=42 and {41,43} are primes.


MATHEMATICA

Table[fl=1; Do[s=(Prime[j])*k; If[PrimeQ[s1]&&PrimeQ[s+1]&&Equal[fl, 1], Print[{j, k}]; fl=0], {k, 1, 2*j^2}], {j, 0, 100}]


PROG

(Haskell)
a071407 n = head [k  k < [2, 4..], let x = k * a000040 n,
a010051' (x  1) == 1, a010051' (x + 1) == 1]
 Reinhard Zumkeller, Feb 14 2013


CROSSREFS

Cf. A071256, A071404A071406, A060256, A060210.
Cf. A071558 (k at every integer).
Cf. A220141, A220142 (record values).
Sequence in context: A011260 A117855 A086442 * A309094 A109859 A128057
Adjacent sequences: A071404 A071405 A071406 * A071408 A071409 A071410


KEYWORD

nonn


AUTHOR

Labos Elemer, May 24 2002


STATUS

approved



