OFFSET
1,1
COMMENTS
Also, number of n-digit primes in A033075.
Appears to be strictly increasing for n >= 8. - Chai Wah Wu, May 31 2017
MAPLE
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:
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
PROG
(Python 3.2 or higher)
from itertools import product, accumulate
from sympy import isprime
def A182781(n):
if n == 1:
return 4
count = 0
for d in [1, 3, 7, 9]:
for elist in product([-1, 1], repeat=n-1):
flist = [str(x) for x in accumulate([d]+list(elist)) if 0 <= x < 10]
if len(flist) == n and flist[-1] != '0' and is_prime(int(''.join(flist[::-1]))):
count += 1
return count # Chai Wah Wu, Jun 05 2017
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Zak Seidov, Feb 01 2011
EXTENSIONS
a(22)-a(24) from Chai Wah Wu, May 31 2017
a(25)-a(32) from Chai Wah Wu, Jun 05 2017
STATUS
approved