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

1,1

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.

Links

Table of n, a(n) for n=1..38.

Example

278 and 287 are two successive semiprimes.

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 *)

Crossrefs

Cf. A001358, A069567.

Sequence in context: A252249 A257368 A056995 * A188446 A251624 A062384

Adjacent sequences: A228132 A228133 A228134 * A228136 A228137 A228138

Keyword

nonn,base,less

Author

Michel Lagneau, Aug 12 2013

Status

approved