A349981 Midpoints k of a pair of twin primes such that sigma(k) is also the midpoint of a pair of twin primes.

6, 30, 462, 1062, 1290, 1482, 1878, 2088, 2790, 3558, 4272, 4338, 6552, 6660, 7308, 8010, 8598, 8820, 10038, 10428, 10530, 10890, 11940, 12042, 12918, 13338, 13758, 16980, 17418, 17580, 18252, 19992, 21588, 22038, 22740, 23742, 25848, 26862, 27738, 32028, 33288, 35730, 37548, 37782, 42180, 42570

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = 6*A202607(n). - Ivan N. Ianakiev, Feb 07 2022

Example

a(3) = 462 is a term because sigma(462) = 1152 and 461, 463, 1151 and 1153 are primes.

Maple

filter:= proc(x) local t;
  if not (isprime(x-1) and isprime(x+1)) then return false fi;
  t:= numtheory:-sigma(x);
  t mod 6 = 0 and isprime(t-1) and isprime(t+1)
end proc:
select(filter, [seq(i, i=6..100000, 6)]);

Crossrefs

Intersection of A014574 and A068017.

Cf. A000203, A202607.

Sequence in context: A111876 A119634 A256545 * A075591 A130075 A066388

Adjacent sequences: A349978 A349979 A349980 * A349982 A349983 A349984

Keyword

nonn

Author

J. M. Bergot and Robert Israel, Feb 06 2022

Status

approved