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Search: id:A060200
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| A060200 |
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Number of Sophie Germain primes <= Prime[2^n]. |
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+0
1
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| 2, 3, 4, 8, 12, 20, 32, 54, 94, 170, 297, 549, 1017, 1895, 3505, 6577, 12388, 23565, 44891, 85922, 164299, 314173, 602624, 1158231, 2232286
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Sophie Germain primes are primes p such that 2p+1 is also prime.
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EXAMPLE
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The first four primes are 2, 3, 5 and 7. Three of these are Sophie Germain primes (since 2*2 + 1 = 5, 2*3 + 1 = 7 and 2*5 + 1 = 11 are prime, but 2*7 + = 15). Therefore the second value in the sequence is 3.
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MATHEMATICA
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<< NumberTheory`NumberTheoryFunctions` cnt = 0; currentPrime = 1; For[ i = 1, i == i, i ++, currentPrime = NextPrime[ currentPrime ]; If[ PrimeQ[ 2*currentPrime + 1 ], cnt++ ]; If[ IntegerQ[ Log[ 2, i ] ], Print[ cnt ] ]; ]
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CROSSREFS
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Cf. A049040.
Sequence in context: A133464 A085635 A013914 this_sequence A057608 A060984 A098348
Adjacent sequences: A060197 A060198 A060199 this_sequence A060201 A060202 A060203
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KEYWORD
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nonn
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AUTHOR
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Alex Healy (ahealy(AT)fas.harvard.edu), Mar 19 2001
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