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 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. 3
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 EXAMPLE 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} MAPLE 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 PROG (Haskell) import Data.List (delete) a125002 n = sum \$ map (a010051' . read) \$                   tail \$ concatMap (f pds) [0 .. length pds - 1] where    pds = show \$ a000040 n    f ws k = [us ++ [y] ++ vs |             let (us, v:vs) = splitAt k ws, y <- delete v "0123456789"] -- Reinhard Zumkeller, Jul 06 2014 (Python) from sympy import isprime, sieve def neighbors(s):     digs = "0123456789"     ham1 = (s[:i]+d+s[i+1:] for i in range(len(s)) for d in digs if d!=s[i])     yield from (h for h in ham1 if h[0] != '0') def a(n):     return sum(1 for s in neighbors(str(sieve[n])) if isprime(int(s))) print([a(n) for n in range(1, 101)]) # Michael S. Branicky, May 09 2022 CROSSREFS Cf. A000040. Sequence in context: A339053 A244584 A092531 * A285245 A098528 A242715 Adjacent sequences:  A124999 A125000 A125001 * A125003 A125004 A125005 KEYWORD nonn,base AUTHOR Zak Seidov, Jan 08 2007 EXTENSIONS Corrected and extended by Hans Havermann and R. J. Mathar, Jan 08 2007 STATUS approved

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Last modified May 28 18:24 EDT 2022. Contains 354122 sequences. (Running on oeis4.)