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 A112729 #9 Jul 21 2025 15:49:38
%S A112729 312,85632,22013952,1443107438592,369435881766912,
%T A112729 24211351590301335552,103986963299971520879061368832
%N A112729 Numbers of the form 2^(k+2)*3*(7*2^k-1) where 7*2^k-1 is prime.
%C A112729 This sequence is a subsequence of A011251 and A011774, namely if m is in the sequence then phi(m)+sigma(m)=3*m (see Comments line of A011251).
%C A112729 Number of digits of all the 20 known terms of this sequence are respectively 3, 5, 8, 13, 15, 20, 30, 109, 11069, 13566, 14787, 15722, 20988, 25263, 40594, 42272, 101802, 104453, 107155 and 219110.
%e A112729 103986963299971520879061368832 is in the sequence because 103986963299971520879061368832=2^(45+2)*3*(7*2^45-1) and 7*2^45-1 is prime.
%t A112729 Do[If[PrimeQ[7*2^n-1], Print[3*2^(n+2)*(7*2^n-1)]], {n, 177}]
%Y A112729 Cf. A001771. A011251, A011774.
%K A112729 easy,nonn
%O A112729 1,1
%A A112729 _Farideh Firoozbakht_, Dec 01 2005