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A352616 Numbers k such that A155085(k) is in A037074. 0

%I #8 Mar 29 2022 19:57:38

%S 7,17,50,71,449,851,881,1467,2591,5123,9521,18167,29817,34859,38027,

%T 39761,52415,84359,90611,92711,106721,147267,179999,204479,206081,

%U 342791,388961,596231,606609,847601,922607,1060307,1256879,1292831,1389671,1590983,1976015,2157227,2169971,2268449,2571911

%N Numbers k such that A155085(k) is in A037074.

%C Numbers k such that k + A000203(k) is the product of a twin prime pair.

%e a(3) = 50 is a term because 50 + A000203(50) = 143 = 11*13 where (11,13) is a twin prime pair.

%p filter:= proc(n) local t,s; t:= n + numtheory:-sigma(n);

%p if t::even or not issqr(t+1) then return false fi;

%p s:= sqrt(t+1);

%p isprime(s+1) and isprime(s-1)

%p end proc:

%p select(filter, [$1..3000000]);

%Y Cf. A000203, A037074, A155085.

%K nonn

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Mar 23 2022

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Last modified March 29 10:44 EDT 2024. Contains 371268 sequences. (Running on oeis4.)