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A182781 Number of n-digit terms in A048398.

%I A182781 #36 Jun 05 2017 19:01:06
%S A182781 4,4,2,1,12,20,35,28,80,114,211,228,736,1214,2101,2536,7799,13830,
%T A182781 22107,27265,82611,144324,259260,354029,901774,1651718,2913981,
%U A182781 3913728,11048656,19782855,33483206,49533124
%N A182781 Number of n-digit terms in A048398.
%C A182781 Also, number of n-digit primes in A033075.
%C A182781 Appears to be strictly increasing for n >= 8. - _Chai Wah Wu_, May 31 2017
%p A182781 A182781aux := proc(Lhig,n) local lsb,a ; if n = 0 then if isprime(Lhig) then    1; else 0; end if; else a := 0 ; lsb := Lhig mod 10 ; if lsb > 0 then a := a + procname(10*Lhig+lsb-1,n-1) ; end if; if lsb < 9 then a := a + procname(10*Lhig+lsb+1,n-1) ; end if; a; end if; end proc:
%p A182781 A182781 := proc(n) if n = 1 then 4; else a := 0 ; for l from 1 to 9 do a := a + A182781aux(l,n-1) ; end do: a ; end if; end proc: # _R. J. Mathar_, Feb 01 2011
%o A182781 (Python 3.2 or higher)
%o A182781 from itertools import product, accumulate
%o A182781 from sympy import isprime
%o A182781 def A182781(n):
%o A182781     if n == 1:
%o A182781         return 4
%o A182781     count = 0
%o A182781     for d in [1,3,7,9]:
%o A182781         for elist in product([-1,1],repeat=n-1):
%o A182781             flist = [str(x) for x in accumulate([d]+list(elist)) if 0 <= x < 10]
%o A182781             if len(flist) == n and flist[-1] != '0' and is_prime(int(''.join(flist[::-1]))):
%o A182781                 count += 1
%o A182781     return count # _Chai Wah Wu_, Jun 05 2017
%Y A182781 Cf. A033075, A048398.
%K A182781 nonn,base,more
%O A182781 1,1
%A A182781 _Zak Seidov_, Feb 01 2011
%E A182781 a(22)-a(24) from _Chai Wah Wu_, May 31 2017
%E A182781 a(25)-a(32) from _Chai Wah Wu_, Jun 05 2017