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 A072296 #12 Jun 03 2013 02:58:29
%S A072296 10,50,532,2314,4628,22578,115024,221960,478302,3340304,22527850,
%T A072296 117335136,1118736102,1564578508,6121287812,7515991946
%N A072296 Least number starting a chain of exactly n consecutive even integers that do not have cototient-inverses.
%C A072296 If the strong Goldbach conjecture (every even number>6 is the sum of at least 2 distinct primes p and q) is true, sequence contains only even values. Since p*q-phi(p*q)=p+q-1 and then every odd number can be expressed as x-phi(x). - _Benoit Cloitre_, Mar 03 2002.
%e A072296 Neither 50 nor 52 have cototient-inverses and since 50 is the first of the two and the least number with this property, a(2) = 50.
%t A072296 a = Table[0, {5*10^7}]; Do[b = n - EulerPhi[n]; If[ b < 5*10^7 + 1, a[[b/2]]++ ], {n, 2, 615437100}] (* used to find a(7) *) Do[ If[ a[[n]] == a[[n + 1]] == a[[n + 2]] == a[[n + 3]] == a[[n + 4]] == a[[n + 5]] == a[[n + 6]] == 0, Print[n]], {n, 1, 10^6}]
%Y A072296 Cf. A005278, A051953, A063512, A063740.
%K A072296 hard,more,nonn
%O A072296 1,1
%A A072296 _Robert G. Wilson v_, Jul 12 2002
%E A072296 a(12)-a(14) from _Donovan Johnson_, Jun 23 2010
%E A072296 a(15)-a(16) from _Donovan Johnson_, Jun 03 2013