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A228135 Smaller of two consecutive semiprimes which are anagrams of each other. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 20 01:01 EST 2022. Contains 350467 sequences. (Running on oeis4.)