A340160 a(n) is the least prime p such that there are exactly n primes of the form p+d where d is a divisor of p-1 or of p+1.

283, 43, 2, 11, 31, 71, 167, 179, 601, 359, 419, 1439, 1559, 3359, 7559, 6047, 5039, 13679, 21001, 13441, 20161, 45361, 15121, 10079, 54001, 41579, 35281, 92399, 99793, 92401, 100801, 65521, 100799, 196561, 241919, 377999, 110879, 451439, 453601, 478801, 498961, 383041, 393121, 262079, 453599

Offset

0,1

Links

Robert Israel, Table of n, a(n) for n = 0..149

Example

a(3) = 11, with 3 primes of the form 11+t where t is a divisor of 10 or 12, namely 13 = 11+2, 17 = 11+6 and 23=11+12.

Maple

f:= proc(p)
     nops(select(t -> isprime(t+p), numtheory:-divisors(p-1) union numtheory:-divisors(p+1)))
end proc:
V:= Array(0..50):
count:= 0: p:= 1:
while count < 51 do
  p:= nextprime(p);
  v:= f(p);
  if v <= 50 and V[v]=0 then count:= count+1; V[v]:= p; fi
od:
convert(V, list);

Crossrefs

Sequence in context: A172627 A172725 A172804 * A334106 A175276 A334096

Adjacent sequences: A340157 A340158 A340159 * A340161 A340162 A340163

Keyword

nonn

Author

J. M. Bergot and Robert Israel, Dec 29 2020

Status

approved