This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A355970 #6 Aug 03 2022 10:49:59 %S A355970 5,7,67,28573,666667,31578949,64912283,66666667,666666667,66666666667, %T A355970 29083665338647,31772053083528493,50819672131147541, %U A355970 4299928432854102613,6811594202898550727,66666666666666666667,29136816792745854416111,46823891622677827205227,66666666666666666666667 %N A355970 Primes p such that p^2 is the concatenation of x and 2*x+1 for some x. %e A355970 a(3) = 67 is a term because it is prime and 67^2 = 4489 is the concatenation of 44 and 2*44+1=89. %p A355970 dcat:=proc(a,b) a*10^(1+ilog10(b))+b end proc: %p A355970 f:= proc(t) local s; %p A355970 if not issqr(t) then return NULL fi; %p A355970 s:=sqrt(t); %p A355970 if isprime(s) then return s fi %p A355970 end proc: %p A355970 map(f, [seq(dcat(x,2*x+1), x=1..5*10^7)]); %Y A355970 Contains A093170. %Y A355970 Cf. A309808, A309828. %K A355970 nonn,base %O A355970 1,1 %A A355970 _J. M. Bergot_ and _Robert Israel_, Jul 21 2022 %E A355970 More terms from _Jinyuan Wang_, Jul 21 2022