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A349981
Midpoints k of a pair of twin primes such that sigma(k) is also the midpoint of a pair of twin primes.
1
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
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.
Sequence in context: A111876 A119634 A256545 * A075591 A130075 A066388
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Feb 06 2022
STATUS
approved