login
A318785
Numbers which are prime if each digit is replaced by its 9's complement.
2
2, 4, 6, 7, 10, 16, 20, 26, 28, 32, 38, 40, 46, 52, 56, 58, 62, 68, 70, 76, 80, 82, 86, 88, 92, 94, 96, 97, 112, 116, 118, 122, 136, 140, 142, 146, 160, 170, 172, 176, 178, 188, 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
OFFSET
1,1
EXAMPLE
32 belongs to this sequence as its 9's complement is 67, which is prime.
PROG
(Python)
nmax=500
def is_prime(num):
if num == 0 or num == 1: return(0)
for k in range(2, num):
if (num % k) == 0:
return(0)
return(1)
def c9(num):
s=str(num)
l=len(str(num))
n=""
for k in range(l):
n = n+str(9-int(s[k]))
return(int(n))
ris = ""
for i in range(2, nmax):
if is_prime(c9(i)):
ris = ris+str(i)+", "
print(ris)
(PARI) complement(n) = my(d=digits(n)); for(k=1, #d, d[k]=9-d[k]); subst(Pol(d), x, 10)
is(n) = ispseudoprime(complement(n)) \\ Felix Fröhlich, Sep 03 2018
CROSSREFS
Cf. A061601 (9's complement of n).
Sequence in context: A026398 A374432 A179003 * A190206 A189287 A189128
KEYWORD
nonn,base
AUTHOR
Pierandrea Formusa, Sep 03 2018
STATUS
approved