cp's OEIS Frontend

A254624 Numbers x such that x = concatenate(a, b) and phi(a) + phi(b) = sigma(x) - x.

%I A254624 #11 Feb 05 2015 07:34:23
%S A254624 49,169,289,611,1751,2171,2231,7921,10751,11479,23153,24367,38551,
%T A254624 38809,49901,99101,116303,143351,229441,268151,271441,306181,357101,
%U A254624 1030301,2014751,2078663
%N A254624 Numbers x such that x = concatenate(a, b) and phi(a) + phi(b) = sigma(x) - x.
%e A254624 49 = concat(4,9); phi(4) = 2, phi(9) = 6, sigma(49) = 57; 2 + 6 = 8 = 57 - 49.
%e A254624 169 = concat(16,9); phi(16) = 8, phi(9) = 6, sigma(169) = 183; 8 + 6 = 14 = 183-169.
%p A254624 with(numtheory); P:=proc(q) local a, b, i, n; for n from 1 to q do
%p A254624 for i from 1 to ilog10(n) do a:=trunc(n/10^i); b:=n-a*10^i;
%p A254624 if phi(a)+phi(b)=sigma(n)-n then print(n); break;
%p A254624 fi; od; od; end: P(10^9);
%Y A254624 Cf. A000010, A000203, A001065, A249065.
%K A254624 nonn,base
%O A254624 1,1
%A A254624 _Paolo P. Lava_, Feb 03 2015