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A061448 a(1) = 2; a(n+1) = smallest prime > a(n) with leading digit equal to final digit of a(n). 3
2, 23, 31, 101, 103, 307, 701, 1009, 9001, 10007, 70001, 100003, 300007, 700001, 1000003, 3000017, 7000003, 30000001, 100000007, 700000001, 1000000007, 7000000001, 10000000019, 90000000019, 90000000023, 300000000077 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Contribution from R. J. Mathar, Feb 15 2012 (Start):

Starting with other primes we find:

3, 31, 101, 103, 307, 701, 1009, 9001, 10007,.. or

5, 53, 307, 701, 1009, 9001, 10007, 70001, 10000.... or

7, 71, 101, 103, 307, 701, 1009, 9001, 10007, 70001 .. or

11, 13, 31, 101, 103, 307, 701, 1009, 9001,.. or

13, 31, 101, 103, 307, 701, 1009, 9001,.. or

17, 71, 101, 103, 307, 701, 1009, 9001, 10007,.. or

19, 97, 701, 1009, 9001, 10007, 70001, 100003,.. (End)

LINKS

Table of n, a(n) for n=1..26.

Index entries for sequences related to final digits of numbers

FORMULA

a(n)=A054262(n-1), n>2. [From R. J. Mathar, Jan 30 2009]

EXAMPLE

a(5) = 103, hence a(6) = 307.

MAPLE

A061448 := proc(n)

    option remember;

    local a, sdig, adgs, ad ;

    if n = 1 then

        2;

    else

        sdig := procname(n-1) mod 10 ;

        a := nextprime(procname(n-1)) ;

        while true do

            adgs := convert(a, base, 10) ;

            ad := op(-1, adgs) ;

            if op(-1, adgs) = sdig then

                if isprime(a) then

                    return a;

                end if;

            elif ad > sdig then

                a := sdig*10^nops(adgs) ;

            elif ad < sdig then

                a := sdig*10^(nops(adgs)-1) ;

            end if;

            a := nextprime(a) ;

        end do:

    end if;

end proc: # R. J. Mathar, Feb 15 2013

MATHEMATICA

a[1]=2; a[n_] := (v=IntegerDigits[a[n-1]]; v1=If[v[[ -1]]>v[[1]], v[[ -1]]*10^(Length[v]-1), If[v[[ -1]]<v[[1]]||Length[v]==1, v[[ -1]]*10^Length[v], a[n-1]]]; For[m=v1+1, !PrimeQ[m], m++ ]; m); Table[a[n], {n, 35}] (* Farideh Firoozbakht, Aug 30 2003 *)

CROSSREFS

Sequence in context: A049568 A049556 A049580 * A115233 A007510 A117242

Adjacent sequences:  A061445 A061446 A061447 * A061449 A061450 A061451

KEYWORD

nonn,base

AUTHOR

Amarnath Murthy, May 03 2001

EXTENSIONS

More terms from Larry Reeves (larryr(AT)acm.org), May 17 2001

Terms from a(18) added by Patrick De Geest, Jun 04 2001.

STATUS

approved

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Last modified October 18 10:28 EDT 2017. Contains 293507 sequences.