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A140515
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Numbers n such that one of floor(10^n * pi) or ceiling(10^n * pi) is prime.
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0
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0, 1, 5, 11, 18, 37, 601, 1901, 2394, 3970, 5826, 16207
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Proofs of the primality of decimal expansions ending at n = 601, 1901 and 2394 are given at marvinrayburns.com. Further terms correspond to probable primes.
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LINKS
| Carlos B. Rivera F. Approximation to pi with primes.
Weisstein, Eric W., Pi Digits
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EXAMPLE
| 10^0*Pi=3.1... =p0. Floor(p0)=3. 3 and is prime, so the first element in the sequence is 0.
10^1*Pi=31.4...=p1. Floor(p1)=31. 31 is prime, so the second element in the sequence is 1.
10^5*Pi=314159.2...=p1. Floor(p1)=314159. 314159 is prime, so the third element in the sequence is 5.
10^11*Pi=314159265358.9...=p2. Ceiling(p2)=314159265359. 314159265359 is prime, so the fourth element in the sequence is 11.
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PROG
| (PARI) isA140515(n)=isprime(bitor(floor(10^n*Pi), 1))
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CROSSREFS
| Sequence in context: A140697 A048253 A102174 * A056996 A102184 A084720
Adjacent sequences: A140512 A140513 A140514 * A140516 A140517 A140518
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KEYWORD
| nonn,base
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AUTHOR
| Marvin Ray Burns (bmmmburns(AT)sbcglobal.net), Jul 01 2008, Jul 02 2008
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