A240678 Primes p such that p*10+k is prime for exactly one value of the digit k.
11, 29, 41, 47, 71, 79, 83, 131, 137, 139, 151, 163, 173, 181, 191, 227, 257, 263, 277, 281, 293, 307, 311, 313, 359, 383, 449, 491, 503, 509, 557, 563, 569, 577, 587, 593, 601, 617, 647, 659, 661, 677, 683, 719, 739, 743, 751, 809, 821, 827, 857, 877, 881
Offset: 1
Examples
11 is in the sequence because 113 is prime, but 111, 117 and 119 are not prime.
Links
- Colin Barker, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
Select[Prime[Range[200]],Total[Boole[PrimeQ[10 #+{1,3,7,9}]]]==1&] (* Harvey P. Dale, Apr 19 2019 *) -
PARI
forprime(p=2, 1500, t=0; forstep(k=1, 9, 2, if(isprime(p*10+k), t++)); if(t==1, print1(p, ", ")))
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Python
from sympy import isprime, primerange def ok(p): return sum(1 for k in [1, 3, 7, 9] if isprime(p*10+k)) == 1 def aupto(limit): return [p for p in primerange(1, limit+1) if ok(p)] print(aupto(881)) # Michael S. Branicky, Nov 29 2021