cp's OEIS Frontend

A318785 Numbers which are prime if each digit is replaced by its 9's complement.

%I A318785 #18 Sep 05 2018 15:12:35
%S A318785 2,4,6,7,10,16,20,26,28,32,38,40,46,52,56,58,62,68,70,76,80,82,86,88,
%T A318785 92,94,96,97,112,116,118,122,136,140,142,146,160,170,172,176,178,188,
%U A318785 190,202,212,226,230,238,242,248,256,260,266,272,280,290,298,308,316,322,326,338,340,346,352,356,358
%N A318785 Numbers which are prime if each digit is replaced by its 9's complement.
%e A318785 32 belongs to this sequence as its 9's complement is 67, which is prime.
%o A318785 (Python)
%o A318785 nmax=500
%o A318785 def is_prime(num):
%o A318785     if num == 0 or num == 1: return(0)
%o A318785     for k in range(2, num):
%o A318785        if (num % k) == 0:
%o A318785            return(0)
%o A318785     return(1)
%o A318785 def c9(num):
%o A318785     s=str(num)
%o A318785     l=len(str(num))
%o A318785     n=""
%o A318785     for k in range(l):
%o A318785         n = n+str(9-int(s[k]))
%o A318785     return(int(n))
%o A318785 ris = ""
%o A318785 for i in range(2,nmax):
%o A318785     if is_prime(c9(i)):
%o A318785        ris = ris+str(i)+","
%o A318785 print(ris)
%o A318785 (PARI) complement(n) = my(d=digits(n)); for(k=1, #d, d[k]=9-d[k]); subst(Pol(d), x, 10)
%o A318785 is(n) = ispseudoprime(complement(n)) \\ _Felix Fröhlich_, Sep 03 2018
%Y A318785 Cf. A061601 (9's complement of n).
%K A318785 nonn,base
%O A318785 1,1
%A A318785 _Pierandrea Formusa_, Sep 03 2018