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 A206770 #9 Jan 12 2013 17:52:04 %S A206770 5,7,11,11,13,17,17,19,23,23,29,29,21,31,37,37,37,41,28,33,47,47,53, %T A206770 53,53,59,59,44,61,67,67,67,71,57,73,79,79,79,83,83,69,89,74,101,68, %U A206770 97,97,85,101,103,107,107,109,113,93,131,127,127,131,127,127,127 %N A206770 Smallest number k such that sigma(k-2*n)=sigma(k)-2*n. %C A206770 Note all k>=1 are considered, even if k-2n<0. If the search space is k>=2n, variants of A020484 and A060264 appear. - _R. J. Mathar_, Jan 12 2013 %e A206770 a(15)=37 because 37 is the minimum number for which sigma(37-2*15)=sigma(7)=8 and sigma(37)-2*15=38-30=8. %p A206770 A206770:=proc(q) %p A206770 local k,n; %p A206770 for n from 1 to q do %p A206770 for k from 1 to q do %p A206770 if sigma(k-2*n)=sigma(k)-2*n then print(k); break; fi; %p A206770 od; od; end: %p A206770 A206770(1000000000); %p A206770 A206770 := proc(n) %p A206770 local k ; %p A206770 for k from 1 do %p A206770 if numtheory[sigma](k-2*n) = numtheory[sigma](k)-2*n then %p A206770 return k; %p A206770 end if; %p A206770 end do: %p A206770 end proc: # _R. J. Mathar_, Jan 12 2013 %Y A206770 Cf. A054906 %K A206770 nonn %O A206770 1,1 %A A206770 _Paolo P. Lava_, Jan 10 2013