The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A239307 Semiprimes n = p*q such that reverse(n)=reverse(p)*reverse(q) where reverse(n) is also semiprime. 1
 4, 6, 9, 22, 26, 33, 39, 55, 62, 77, 93, 121, 143, 169, 187, 202, 226, 262, 303, 339, 341, 393, 505, 622, 626, 707, 781, 933, 939, 961, 1111, 1177, 1243, 1313, 1441, 1469, 1661, 1717, 1991, 2042, 2062, 2066, 2206, 2402, 2426, 2446, 2462, 2602, 2642, 3063, 3093 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Subsequence of A001358. LINKS Giovanni Resta, Table of n, a(n) for n = 1..10000 EXAMPLE 1469 = 13*113 is in the sequence because reverse(1469)=reverse(13)*reverse(113) => 9641 = 31*311 where 31 and 311 are prime numbers. MAPLE with(numtheory):lst:={}:T1:=array(1..300):T2:=array(1..300):k:=0:    for n from 1 to 1000 do:        p:=ithprime(n):xp:=convert(p, base, 10):        np:=nops(xp):sp:=sum('xp[np-i+1]*10^(i-1)', 'i'=1..np):          if type(sp, prime)=true          then          k:=k+1:T1[k]:=p:T2[k]:=sp:          else          fi:     od:          for i from 1 to k do:            for j from i to k do:               x:=T1[i]*T1[j]:y:=convert(x, base, 10):n2:=nops(y):               s:=sum('y[n2-i+1]*10^(i-1)', 'i'=1..n2):               if T2[i]*T2[j]=s               then               lst:=lst union {x}:               else               fi:           od:         od:         print(lst): CROSSREFS Cf. A007500, A001358. Sequence in context: A032817 A115681 A257842 * A137253 A035135 A046338 Adjacent sequences:  A239304 A239305 A239306 * A239308 A239309 A239310 KEYWORD nonn,base AUTHOR Michel Lagneau, Mar 15 2014 STATUS approved

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

Last modified August 10 00:32 EDT 2022. Contains 356026 sequences. (Running on oeis4.)