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A182781 Number of n-digit terms in A048398. 2
4, 4, 2, 1, 12, 20, 35, 28, 80, 114, 211, 228, 736, 1214, 2101, 2536, 7799, 13830, 22107, 27265, 82611, 144324, 259260, 354029, 901774, 1651718, 2913981, 3913728, 11048656, 19782855, 33483206, 49533124 (list; graph; refs; listen; history; text; internal format)
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

LINKS

Table of n, a(n) for n=1..32.

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

Cf. A033075, A048398.

Sequence in context: A153163 A168455 A300153 * A291085 A193556 A120438

Adjacent sequences:  A182778 A182779 A182780 * A182782 A182783 A182784

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

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Last modified July 21 00:39 EDT 2019. Contains 325189 sequences. (Running on oeis4.)