A078500 Primes occurring only twice in a decade.
23, 29, 31, 37, 53, 59, 61, 67, 83, 89, 151, 157, 163, 167, 173, 179, 233, 239, 251, 257, 263, 269, 271, 277, 281, 283, 331, 337, 347, 349, 353, 359, 373, 379, 383, 389, 401, 409, 443, 449, 491, 499, 503, 509, 521, 523, 541, 547, 563, 569, 571, 577, 593, 599
Offset: 1
Links
- Alois P. Heinz, Table of n, a(n) for n = 1..10000
Crossrefs
Cf. A078494.
Programs
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Magma
&cat [PrimesInInterval(10*n+1, 10*n+9): n in [0..50] | #PrimesInInterval(10*n+1, 10*n+9) eq 2]; // Bruno Berselli, Sep 05 2012
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Mathematica
Select[Table[Prime[Range[PrimePi[n*10]+1,PrimePi[n*10+10]]],{n,60}],Length[ #] == 2&]//Flatten (* Harvey P. Dale, Aug 09 2020 *) -
PARI
decade2pr(n1,n2) = { if(n1==0,n1=10); forstep(x=n1,n2,10, if(isprime(x+1) && isprime(x+3) && !isprime(x+7) && !isprime(x+9), print1(x+1" "x+3" ");); if(isprime(x+1) && isprime(x+7) && !isprime(x+3) && !isprime(x+9), print1(x+1" "x+7" ");); if(isprime(x+1) && isprime(x+9) && !isprime(x+3) && !isprime(x+7), print1(x+1" "x+9" ");); if(isprime(x+3) && isprime(x+7) && !isprime(x+1) && !isprime(x+9), print1(x+3" "x+7" ");); if(isprime(x+3) && isprime(x+9) && !isprime(x+1) && !isprime(x+7), print1(x+3" "x+9" ");); if(isprime(x+7) && isprime(x+9) && !isprime(x+1) && !isprime(x+3), print1(x+7" "x+9" ");); ); }
Extensions
Offset changed to 1 by Alois P. Heinz, Jul 22 2014
Comments