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A104045 Numbers k such that k9 is prime and k is a multiple of ten.

%I A104045 #26 Jan 19 2024 20:02:31
%S A104045 10,40,50,70,80,100,110,140,160,170,230,260,290,310,320,370,440,490,
%T A104045 500,520,530,670,710,730,800,820,860,910,920,1000,1070,1090,1190,1210,
%U A104045 1240,1280,1300,1310,1330,1370,1400,1580,1720,1750,1760,1790,1900,1930,1960,1970,2050,2080,2210
%N A104045 Numbers k such that k9 is prime and k is a multiple of ten.
%H A104045 Michael S. Branicky, <a href="/A104045/b104045.txt">Table of n, a(n) for n = 1..10000</a>
%e A104045 If k =  10, then k9 =  109 (prime).
%e A104045 If k = 160, then k9 = 1609 (prime).
%e A104045 If k = 320, then k9 = 3209 (prime).
%p A104045 select(n-> isprime(10*n+9), [10*i$i=1..300])[];  # _Alois P. Heinz_, Jan 19 2024
%t A104045 Select[Range[10,2210,10],PrimeQ[FromDigits[Prepend[{9},#]]]&] (* _James C. McMahon_, Jan 19 2024 *)
%o A104045 (Python)
%o A104045 from sympy import isprime
%o A104045 from itertools import count, islice
%o A104045 def agen(): yield from (k for k in count(10, 10) if isprime(10*k+9))
%o A104045 print(list(islice(agen(), 53))) # _Michael S. Branicky_, Jan 19 2024
%Y A104045 Cf. A030433, A008592, A102700, A166560 (resulting primes).
%K A104045 base,nonn
%O A104045 1,1
%A A104045 _Parthasarathy Nambi_, Mar 01 2005