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A125002
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Let p = prime(n); a(n) = number of primes q with same number of digits as p that can be obtained from p by changing one digit.
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1
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3, 3, 3, 3, 7, 8, 7, 7, 6, 5, 5, 5, 6, 7, 6, 6, 5, 5, 5, 6, 7, 6, 6, 5, 4, 10, 8, 11, 11, 6, 8, 9, 9, 10, 6, 7, 11, 9, 9, 8, 7, 6, 10, 9, 11, 9, 7, 8, 7, 6, 7, 7, 7, 7, 8, 9, 5, 7, 7, 7, 9, 6, 8, 6, 7, 8, 5, 8, 9, 6, 7, 6, 8, 7, 6, 8, 4, 8, 8, 10, 8, 6, 9, 6, 11, 5, 8, 7, 8, 8, 7, 7, 5, 8, 8, 5, 7, 5, 6, 6
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..100.
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EXAMPLE
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The 5th prime 11 leads to 7 other primes: 13,17,19,31,41,61,71, hence a(5)=7.
a(6)=8, p=13, q={11,17,19,23,43,53,73,83}
a(7)=7, p=17, q={11,13,19,37,47,67,97}
a(8)=7, p=19, q={11,13,17,29,59,79,89}
a(9)=6, p=23, q={29,13,43,53,73,83}
a(10)=5, p=29, q={23,19,59,79,89}
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MAPLE
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A125002 := proc(n) local p, digs, res, r, d; p := ithprime(n) ; digs := convert(p, base, 10) ; res := 0 ; for d from 1 to nops(digs) do for r from 0 to 9 do if r <> op(d, digs) and ( d <> nops(digs) or r > 0) then q := p-(op(d, digs)-r)*10^(d-1) ; if isprime(q) then res := res+1 ; fi ; fi ; od ; od ; RETURN(res) ; end ; for n from 1 to 100 do printf("%d, ", A125002(n)) ; od ; - R. J. Mathar, Jan 13 2007
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CROSSREFS
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Sequence in context: A079084 A092323 A092531 * A098528 A078229 A222292
Adjacent sequences: A124999 A125000 A125001 * A125003 A125004 A125005
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KEYWORD
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nonn,base
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AUTHOR
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Zak Seidov, Jan 08 2007
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EXTENSIONS
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Corrected and extended by Hans Havermann and R. J. Mathar, Jan 08 2007
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STATUS
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approved
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