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A066753
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a(n) = least natural number k such that n + sum_{1,...,k} Prime[i] is prime if such k exists; = 0 otherwise.
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4
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1, 2, 1, 20, 1, 2, 3, 2, 1, 10, 1, 2, 3, 2, 1, 16, 1, 2, 3, 4, 1, 10, 17, 2, 5, 2, 1, 10, 1, 4, 3, 2, 3, 10, 1, 2, 3, 2, 1, 16, 1, 2, 3, 4, 1, 18, 17, 2, 3, 4, 1, 10, 41, 2, 5, 2, 1, 16, 1, 6, 3, 2, 3, 10, 1, 2, 9, 2, 1, 10, 1, 4, 3, 2, 5, 16, 1, 2, 3, 4, 1, 10, 17, 2, 5, 4, 1, 20, 43, 4, 3, 2, 3, 10
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Does a(n) ever take 0 as a value?
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,1000
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EXAMPLE
| 20 + (2 + 3 + 5 + 7) = 37, a prime and 4 consecutive primes starting with 2 are required to achieve this. So a(20) = 4.
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MATHEMATICA
| nt = 200; a = Table[0, {i, 1, nt}]; For[n = 1, n <= nt, n++, {i = 1; s = n + Prime[i]; While[Not[PrimeQ[s]] && (i < 1000), {i++; s = s + Prime[i]}]; a[[n]] = i}]; a
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PROG
| (PARI) { for (n=1, 1000, k=0; b=0; s=n; while(b==0, k++; s+=prime(k); if (isprime(s), b=1)); write("b066753.txt", n, " ", k) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Mar 22 2010]
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CROSSREFS
| Sequence in context: A012901 A013021 A012907 * A103244 A185169 A012927
Adjacent sequences: A066750 A066751 A066752 * A066754 A066755 A066756
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 16 2002
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EXTENSIONS
| Edited by John W. Layman (layman(AT)math.vt.edu), Jan 23 2002
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