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 A074998 Composite numbers which are sandwiched between two numbers having the same unordered canonical form. 2

%I

%S 4,6,12,18,30,34,42,51,55,56,60,72,86,92,94,102,108,138,142,144,150,

%T 160,180,184,186,192,198,202,204,214,216,218,220,228,236,240,243,248,

%U 249,266,270,282,300,302,304,312,320,322,328,340,341,348,392,394,412

%N Composite numbers which are sandwiched between two numbers having the same unordered canonical form.

%C The average of twin primes is a member.

%H Amiram Eldar, <a href="/A074998/b074998.txt">Table of n, a(n) for n = 1..10000</a>

%e 34 is sandwiched between 33 and 35 which are of the form p*q where p and q are primes.

%p k := 0: for j from 2 to 5000 do if not isprime(j) then a := ifactors(j-1): b := ifactors(j+1): if sort([seq(a[2][i][2],i= 1..nops(a[2]))])= sort([seq(b[2][i][2],i= 1..nops(b[2]))]) then k := k+1: c[k] := j: fi: fi: od: seq(c[i],i= 1..k);

%Y Cf. A074997, A061715, A074460.

%K nonn

%O 1,1

%A _Amarnath Murthy_, Aug 21 2002

%E More terms from _Sascha Kurz_, Aug 22 2002

%E Offset corrected by _Amiram Eldar_, Jan 02 2020

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Last modified August 5 11:48 EDT 2021. Contains 346467 sequences. (Running on oeis4.)