Search: id:A125002
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%I A125002
%S A125002 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,
%T A125002 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,
%U A125002 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
%N A125002 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.
%e A125002 The 5th prime 11 leads to 7 other primes: 13,17,19,31,41,61,71, hence 
               a(5)=7.
%e A125002 a(6)=8, p=13, q={11,17,19,23,43,53,73,83}
%e A125002 a(7)=7, p=17, q={11,13,19,37,47,67,97}
%e A125002 a(8)=7, p=19, q={11,13,17,29,59,79,89}
%e A125002 a(9)=6, p=23, q={29,13,43,53,73,83}
%e A125002 a(10)=5, p=29, q={23,19,59,79,89}
%p A125002 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 (mathar(AT)strw.leidenuniv.nl), 
               Jan 13 2007
%Y A125002 Sequence in context: A079084 A092323 A092531 this_sequence A098528 A078229 
               A007428
%Y A125002 Adjacent sequences: A124999 A125000 A125001 this_sequence A125003 A125004 
               A125005
%K A125002 nonn,base
%O A125002 1,1
%A A125002 Zak Seidov, Jan 08 2007
%E A125002 Corrected and extended by Hans Havermann (pxp(AT)rogers.com) and R. J. 
               Mathar (mathar(AT)strw.leidenuniv.nl), Jan 08 2007

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