This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A271431 Primes with at least four digits that remain prime when any two adjacent groups of two digits switch places. 0
 1103, 1109, 1123, 1163, 1181, 1193, 1301, 1303, 1319, 1321, 1327, 1361, 1777, 1783, 1907, 1913, 1931, 1933, 1949, 1951, 1979, 1987, 1993, 1997, 2113, 2131, 2161, 2311, 2333, 2339, 2347, 2377, 2381, 2389, 2393, 2399, 2707, 2713, 2729, 2741, 2777, 2791, 2909 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A 4-digit prime abcd is a member if cdab is also a prime. c can be zero. A 5-digit prime abcde is a member if both cdabe and adebc are primes. Again c can be zero, but not (of course) a. LINKS PROG (PARI) eva(n) = subst(Pol(n), x, 10) switchdigits(n, k) = my(d=digits(n), v=vector(2)); v[1]=d[k]; v[2]=d[k+1]; d[k]=d[k+2]; d[k+1]=d[k+3]; d[k+2]=v[1]; d[k+3]=v[2]; eva(d) is(n) = my(i=0); for(k=1, #Str(n)-3, if(ispseudoprime(switchdigits(n, k)), i++)); if(i==#Str(n)-3, return(1), return(0)) forprime(p=1000, 2000, if(is(p), print1(p, ", "))) CROSSREFS Sequence in context: A178407 A178348 A250796 * A272754 A060519 A197422 Adjacent sequences:  A271428 A271429 A271430 * A271432 A271433 A271434 KEYWORD nonn,base AUTHOR Felix FrÃ¶hlich, Apr 07 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 14 05:36 EST 2019. Contains 329978 sequences. (Running on oeis4.)