A293478 Composite numbers k = concat(x,LSD(k)) such that k' = x', where k' is the arithmetic derivative of k.

17251, 109999, 112639, 130733, 269119, 318293, 390319, 463669, 1319519, 1726541, 1841839, 2010719, 2013187, 2311919, 5780221, 6493519, 7355839, 7533599, 10668773, 12652639, 14650639, 14951999, 21098459, 21500071, 25167845, 31008319, 35807999, 38687599, 39458719

Offset

1,1

Links

Table of n, a(n) for n=1..29.

Example

17251' = 1725' = 1340, so 17251 is a term.
109999' = 10999' = 664, so 109999 is a term.

Maple

with(numtheory): P:=proc(q) local a, k, n, p, x, y; for n from 2 to q do
if not isprime(n) then x:=trunc(n/10); a:=x*add(op(2, p)/op(1, p), p=ifactors(x)[2]);
if n*add(op(2, p)/op(1, p), p=ifactors(n)[2])=a then print(n); fi; fi; od; end: P(10^6);

Crossrefs

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

Sequence in context: A233993 A043621 A334310 * A076774 A236447 A094413

Adjacent sequences: A293475 A293476 A293477 * A293479 A293480 A293481

Keyword

nonn,base,easy

Author

Paolo P. Lava, Oct 10 2017

Status

approved