A018847 Strobogrammatic primes: the same upside down (calculator-style numerals).

2, 5, 11, 101, 151, 181, 619, 659, 6229, 10501, 12821, 15551, 16091, 18181, 19861, 60209, 60509, 61519, 61819, 62129, 116911, 119611, 160091, 169691, 191161, 196961, 605509, 620029, 625529, 626929, 650059, 655559, 656959, 682289, 686989, 688889

Offset

1,1

Comments

This is the subsequence of primes in A018846. - M. F. Hasler, May 05 2012

Links

M. F. Hasler, Table of n, a(n) for n = 1..648

Mathematica

lst = {}; fQ[n_] := Block[{allset = {0, 1, 2, 5, 6, 8, 9}, id = IntegerDigits@n}, Union@ Join[id, allset] == allset && Reverse[id /. {6 -> 9, 9 -> 6}] == id]; Do[ If[ PrimeQ@n && fQ@n, AppendTo[lst, n]], {n, 700000}]; lst (* Robert G. Wilson v, Feb 27 2007 *)

Prog

(PARI) {write("/tmp/b018847.txt", "1 2\n2 5"); c=2; s2=[0, 1, 2, 5, 6, 8, 9]; s=[0, 1, 2, 5, 8]; s1=[0, 1, 2, 5, 9, 8, 6]; for(n=2, 9, p1=vector( (n+1)\2, i, 10^(i-1)); p2=vector( (n+1)\2, i, 10^(n-i)); forvec( v=vector((n+1)\2, i, if( i>1, [ 1, if( i>n\2, #s, #s1)], [2, 5])), v[1]==3 & v[1]=5; ispseudoprime( t=sum(i=1, n\2, p1[i]*s1[v[i]]+p2[i]*s2[v[i]] ) +if(n%2, p1[#p1]*s[v[#v]] )) & /* print1(t", ") */ write("/tmp/b018847.txt", c++" "t)))} \\ - M. F. Hasler, Apr 26 2012
(PARI) is_A018847(n, t=Vec("012..59.86"))={ isprime(n) & apply(x->t[eval(x)+1], n=Vec(Str(n)))==vecextract(n, "-1..1") } \\ - M. F. Hasler, May 05 2012

Crossrefs

Cf. A007597 (more restrictive version not allowing digits 2 or 5).

Sequence in context: A267527 A286453 A309375 * A178318 A134996 A134998

Adjacent sequences: A018844 A018845 A018846 * A018848 A018849 A018850

Keyword

nonn,base

Author

David W. Wilson

Status

approved