A156343 Primes with equal number of prime and nonprime digits.
13, 17, 29, 31, 43, 47, 59, 67, 71, 79, 83, 97, 1033, 1123, 1153, 1213, 1217, 1229, 1231, 1259, 1279, 1283, 1297, 1303, 1307, 1321, 1367, 1423, 1427, 1433, 1453, 1531, 1543, 1559, 1567, 1571, 1579, 1583, 1597, 1627, 1637, 1657, 1721, 1747, 1759, 1783, 1787
Offset: 1
Examples
13 (1=nonprime, 3=prime) = a(1).
Links
- Michael S. Branicky, Table of n, a(n) for n = 1..10000
Programs
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Maple
A109066c := proc(n) nops(convert(n,base,10))-A109066(n) ; end: A109066 := proc(n) local dgs,a ; dgs := convert(n,base,10) ; a := 0 ; for i in dgs do if isprime(i) then a := a+1 ; fi; od: a ; end: for i from 1 to 400 do p := ithprime(i) ; if A109066(p) = A109066c(p) then printf("%d,",p) ; fi; od: # R. J. Mathar, Feb 09 2009
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Mathematica
Select[Prime[Range[5,300]],Length[Select[IntegerDigits[#],PrimeQ]]==Length[ Select[ IntegerDigits[ #],!PrimeQ[ #]&]]&] (* Harvey P. Dale, Dec 15 2022 *)
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Python
from sympy import isprime def ok(n): if not isprime(n): return False s, counts = str(n), [0, 0] for c in s: counts[int(c in "2357")] += 1 return counts[0] == counts[1] print([k for k in range(10**4) if ok(k)]) # Michael S. Branicky, Apr 23 2024
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