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A076623 Total number of left truncatable primes (without zeros) in base n. 11
0, 3, 16, 15, 454, 22, 446, 108, 4260, 75, 170053, 100, 34393, 9357, 27982, 362, 14979714, 685, 3062899, 59131, 1599447, 1372, 1052029701, 10484, 7028048, 98336, 69058060, 3926 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

COMMENTS

Approximation of a(b) by (PARI) code: l(b)=c=b*(b-1)/log(b)/eulerphi(b);\ return(floor((primepi(b)-omega(b))*exp(c)/c));

a(24)=1052029701 based on strong BPSW pseudoprimes. Other terms up to a(29) use proved primes. - Martin Fuller, Nov 24 2008

LINKS

Table of n, a(n) for n=2..29.

Angell, I. O. and Godwin, H. J., On Truncatable Primes, Math. Comput. 31, 265-267, 1977.

Martin Fuller, Table of n, a(n) for n= 2..53, with question marks where unknown

Hans Havermann, A076623 Decomposed

Index entries for sequences related to truncatable primes

MAPLE

Lton := proc(L, b) add( op(i, L)*b^(i-1), i=1..nops(L)) ; end proc:

A076623rec := proc(L, b) local a, d, Lext, p ; a := 0 ; for d from 1 to b-1 do Lext := [op(L), d] ; p := Lton(Lext, b) ; if isprime(p) then a := a+1 ;  a := a+procname(Lext, b) ; end if; end do: a ; end proc:

A076623 := proc(b) A076623rec([], b) ; end proc:

for b from 2 do print(b, A076623(b)) ; end do: # R. J. Mathar, Jun 01 2011

PROG

(PARI code from Robert Gerbicz, Oct 31 2008)

f(b)=ct=0; A=[0]; n=-1; L=1; while(L, n++; B=vector(L*b); M=0; \

for(i=1, L, for(j=1, b-1, x=A[i]+j*b^n; if(isprime[x], M++; B[M]=x; ct++))); \

L=M; A=vector(L, i, B[i])); return(ct)

CROSSREFS

Cf. A024779, A024780, A024781, A024782, A024783, A024784, A024785, A076586, A103443, A103463.

Sequence in context: A213847 A195883 A272329 * A068516 A219508 A032922

Adjacent sequences:  A076620 A076621 A076622 * A076624 A076625 A076626

KEYWORD

nonn,base

AUTHOR

Martin Renner, Oct 22 2002, Nov 03 2002, Sep 24 2007, Feb 20 2008, Apr 20 2008

EXTENSIONS

a(12) corrected from 170051 to 170053 by Martin Fuller, Oct 31 2008

Correction of a(18) and approximation for a(n). - Robert Gerbicz, Nov 02 2008

a(24) - a(29) from Martin Fuller, Nov 24 2008

Entries in a-file corrected by N. J. A. Sloane, Jun 02 2011

STATUS

approved

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Last modified March 27 18:32 EDT 2017. Contains 284177 sequences.