OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
Walter A. Kehowski, D Numbers.
FORMULA
a(n)=n-th number x such that x+d+1 is composite for all divisors d of x.
EXAMPLE
a(9)=46=2*23 since 46+1+1=48=16*3, 46+2+1=49=7*7, 46+23+1=70=2*5*7, 46+46+1=93=3*31.
MAPLE
with(numtheory): cnt:=0: L:=[]: for w to 1 do for n from 1 while cnt<100 do dn:=divisors(n); Q:=map(z-> n+z+1, dn); if andmap(z-> not isprime(z), Q) then cnt:=cnt+1; L:=[op(L), [cnt, n]]; fi; od od; L;
MATHEMATICA
Select[Range[300], AllTrue[#+1+Divisors[#], CompositeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Sep 05 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Walter Kehowski, Aug 09 2006
STATUS
approved