A228135 Smaller of two consecutive semiprimes which are anagrams of each other.

278, 1945, 2545, 4045, 5389, 9134, 9289, 12634, 17678, 23578, 25034, 25178, 27289, 32245, 32689, 34889, 35078, 40234, 42289, 47578, 47789, 48979, 50579, 51434, 51589, 55534, 55634, 55934, 57289, 57779, 69334, 69478, 70178, 70234, 71945, 71989, 72134, 76345

Offset: 1

Author

Michel Lagneau, Aug 12 2013

Keywords

• nonn
• base
• less

Comments

Given the n-th semiprime, it is occasionally possible to form the (n+1)-th semiprime using the same digits in a different order.

"Anagram" means that both semiprimes must not only use the same digits but must use each digit the same number of times.

Examples

			278 and 287 are two successive semiprimes.
		

Crossrefs

Cf. A001358, A069567.

Programs

Maple

with(numtheory):T:=array(1..50000):k:=0:for i from 1 to 200000 do:if bigomega(i)=2 then k:=k+1:T[k]:=i:else fi:od:for n from 1 to k-1 do:p1:=T[n]:p2:= T[n+1]:pp1:=convert(p1,base,10): pp2:=convert(p2,base,10):n1:=sort(pp1):n2:=sort(pp2): if n1=n2 then printf(`%d, `,p1):else fi:od:

Mathematica

range[n_Integer]:=Select[Range@n,PrimeOmega@#==2&];
anagramQ[l_List]:=(l1=Sort@#&/@IntegerDigits@l;l1[[1]]==l1[[2]]);
Select[Partition[range@100000,2,1],anagramQ]\[Transpose]//First (* Hans Rudolf Widmer, Oct 06 2021 *)