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 A076623 Total number of left truncatable primes (without zeros) in base n. 14
 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)); - Robert Gerbicz, Nov 02 2008 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. I. O. Angell and H. J. Godwin, On Truncatable Primes, Math. Comput. 31, 265-267, 1977. Michael S. Branicky, String-based Python Program 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) 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) \\ Robert Gerbicz, Oct 31 2008 (Python) # works for all n; link has faster string-based version for n < 37 from sympy import isprime, primerange from sympy.ntheory.digits import digits def fromdigits(digs, base): return sum(d*base**i for i, d in enumerate(digs)) def a(n): prime_lists, an = [(p, ) for p in primerange(1, n)], 0 while len(prime_lists) > 0: an += len(prime_lists) candidates = set(p+(d, ) for p in prime_lists for d in range(1, n)) prime_lists = [c for c in candidates if isprime(fromdigits(c, n))] return an print([a(n) for n in range(2, 12)]) # Michael S. Branicky, Apr 27 2022 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,more 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 a(18) corrected by 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 November 30 21:14 EST 2023. Contains 367462 sequences. (Running on oeis4.)