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Search: id:A080821
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| A080821 |
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Primes in the accumulated tally of steps in the x+1 problem: Repeat, if x is even divide by 2 else add 1 until 1 is reached. |
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+0
1
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| 11, 19, 29, 41, 83, 113, 167, 173, 199, 307, 367, 383, 463, 487, 521, 607, 617, 691, 701, 769, 809, 881, 929, 967, 977, 1423, 1567, 1579, 1627, 1753, 2029, 2063, 2087, 2207, 2239, 2251, 2297, 2341, 2383, 2393, 2467, 2477, 2579, 2657, 2789, 2833, 3001, 3533
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Sum of reciprocals for the x+1 problem is around .318 Sum of reciprocals for the 3x+1 problem is around .1116
The number of steps for the x+1 problem starting at n is A061313(n). The partial sums of A061313 are the sequence 0, 1, 4, 6, 11, 15, 19, 22, 29, 35, 41,... Selecting the primes from these builds the current sequence. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Feb 01 2008
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PROGRAM
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(PARI) xpcount(n, p) = { ct=0; sr=0; for(x=1, n, p1 = x; while(p1>1, if(p1%2==0, p1/=2; ct++, p1 = p1*p+1; ct++) ); if(isprime(ct), print1(ct" "); sr+=1.0/ct) ); print(); print(sr) }
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CROSSREFS
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Sequence in context: A053032 A034099 A034109 this_sequence A094517 A049719 A122869
Adjacent sequences: A080818 A080819 A080820 this_sequence A080822 A080823 A080824
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Mar 26 2003
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