



0, 1, 2, 3, 4, 5, 6, 11, 13, 24, 66, 68, 75, 167, 171, 172, 287, 310, 352, 384, 457, 564, 590, 616, 620, 643, 849
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,3


LINKS

Table of n, a(n) for n=1..27.


FORMULA

a(n)=k such that A088257(n)=A002110(k).


EXAMPLE

3 is in the sequence because primorial p_3# = 2 * 3 * 5 = 30 has two prime neighbors 29 and 31.
4 is in the sequence because primorial p_4# = 2 * 3 * 5 * 7 = 210 has one prime neighbor 211; 209 = 11 * 19.
7 is not in the sequence because the product of the smallest 7 primes has two composite neighbors.


MAPLE

A:= NULL:
P:= 1: p:= 1;
for n from 1 to 700 do
p:= nextprime(p);
P:= P*p;
if isprime(P+1) or isprime(P1) then A:= A, n fi
od:
A; # Robert Israel, Aug 03 2016


MATHEMATICA

Select[Range[0, 600], Total@ Boole@ PrimeQ@ {#  1, # + 1} > 0 &@ Apply[Times, Prime@ Range@ #] &] (* Michael De Vlieger, Aug 03 2016 *)


CROSSREFS

Cf. A002110, A088257.
Sequence in context: A082657 A108378 A084588 * A075073 A157420 A221471
Adjacent sequences: A088408 A088409 A088410 * A088412 A088413 A088414


KEYWORD

more,nonn


AUTHOR

Ray Chandler, Sep 29 2003


EXTENSIONS

a(22)a(27) from Michael De Vlieger, Aug 03 2016


STATUS

approved



