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A078500
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Primes occurring only twice in a decade.
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0
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| Only 6 such primes will occur in the 21st century.
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PROG
| (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" "); ); ); }
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CROSSREFS
| Sequence in context: A166063 A049483 A112681 * A155913 A153631 A082943
Adjacent sequences: A078497 A078498 A078499 * A078501 A078502 A078503
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KEYWORD
| easy,nonn
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AUTHOR
| Cino Hilliard (hillcino368(AT)gmail.com), Jan 04 2003
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