A293478 - OEIS

%I #9 Oct 13 2017 06:13:09

%S 17251,109999,112639,130733,269119,318293,390319,463669,1319519,

%T 1726541,1841839,2010719,2013187,2311919,5780221,6493519,7355839,

%U 7533599,10668773,12652639,14650639,14951999,21098459,21500071,25167845,31008319,35807999,38687599,39458719

%N Composite numbers k = concat(x,LSD(k)) such that k' = x', where k' is the arithmetic derivative of k.

%e 17251' = 1725' = 1340, so 17251 is a term.

%e 109999' = 10999' = 664, so 109999 is a term.

%p with(numtheory): P:=proc(q) local a,k,n,p,x,y; for n from 2 to q do

%p if not isprime(n) then x:=trunc(n/10); a:=x*add(op(2, p)/op(1,p), p=ifactors(x)[2]);

%p if n*add(op(2, p)/op(1, p), p=ifactors(n)[2])=a then print(n); fi; fi; od; end: P(10^6);

%Y Cf. A010879 (LSD), A003415 (arithmetic derivative).

%K nonn,base,easy

%O 1,1

%A _Paolo P. Lava_, Oct 10 2017