OFFSET
1,1
COMMENTS
Similar to A120712 which uses the proper divisors of n.
LINKS
Klaus Brockhaus Table of n, a(n) for n = 1..1000 (first 250 terms from Paolo P. Lava)
EXAMPLE
The anti-divisors of 40 are 3, 9, 16, 27, and 391627 is prime, hence 40 is in the sequence.
MAPLE
P:=proc(i) local a, b, c, d, k, n, s, v; v:=array(1..200000);
for n from 3 by 1 to i do k:=2; b:=0;
while k<n do if (k mod 2)=0 then
if (n mod k)>0 and (2*n mod k)=0 then b:=b+1; v[b]:=k; fi;
else
if (n mod k)>0 and (((2*n-1) mod k)=0 or ((2*n+1) mod k)=0) then
b:=b+1; v[b]:=k; fi; fi; k:=k+1; od; a:=v[1];
for s from 2 to b do a:=a*10^floor(1+evalf(log10(v[s])))+v[s]; od;
if isprime(a) then print(n); fi;
od; end: P(10^6);
MATHEMATICA
antiDivisors[n_Integer] := Cases[Range[2, n - 1], _?(Abs[Mod[n, #] - #/2] < 1 &)]; a191647[n_Integer] := Select[Range[n],
PrimeQ[FromDigits[Flatten[IntegerDigits /@ antiDivisors[#]]]] &]; a191647[1350] (* Michael De Vlieger, Aug 09 2014, "antiDivisors" after Harvey P. Dale at A066272 *)
PROG
(Python)
from sympy import isprime
[n for n in range(3, 10**4) if isprime(int(''.join([str(d) for d in range(2, n) if n%d and 2*n%d in [d-1, 0, 1]])))] # Chai Wah Wu, Aug 08 2014
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, Jun 10 2011
EXTENSIONS
a(618) corrected in b-file by Paolo P. Lava, Feb 28 2018
STATUS
approved