OFFSET
1,1
EXAMPLE
373763 = 13*28751, 28751-13 = 28738 = 2*14369, 14369-2 = 14367 = 3*4789, 4789-3 = 4786 = 2*2393, 2393-2 = 2391 = 3*797, 797-3 = 794 = 2*397, 397-2 = 395 = 5*79 = 79-5 = 74 = 2*37, 37-2 = 35 = 5*7 but 7-5 = 2 is not a squarefree semiprime.
2276543 = 79*28817, 28817-79 = 28738 = 2*14369, 14369-2 = 14367 = 3*4789, 4789-3 = 4786 = 2*2393, 2393-2 = 2391 = 3*797, 797-3 = 794 = 2*397, 397-2 = 395 = 5*79 = 79-5 = 74 = 2*37, 37-2 = 35 = 5*7 but 7-5 = 2 is not a squarefree semiprime.
MAPLE
with(numtheory): P:=proc(n, h) local a, j, ok; ok:=1; a:=n; for j from 1 to h do if issqrfree(a) and nops(factorset(a))=2 then a:=ifactors(a)[2]; a:=a[1][1]-a[2][1]; else ok:=0; break; fi; od; if ok=1 then n; fi; end: seq(P(i, 9), i=1..10^8);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Dec 21 2017
STATUS
approved