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A074998 Composite numbers which are sandwiched between two numbers having the same unordered canonical form. 1
4, 6, 12, 18, 30, 34, 42, 51, 55, 56, 60, 72, 86, 92, 94, 102, 108, 138, 142, 144, 150, 160, 180, 184, 186, 192, 198, 202, 204, 214, 216, 218, 220, 228, 236, 240, 243, 248, 249, 266, 270, 282, 300, 302, 304, 312, 320, 322, 328, 340, 341, 348, 392, 394, 412 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

The average of twin primes is a member.

LINKS

Table of n, a(n) for n=0..54.

EXAMPLE

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

MAPLE

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);

CROSSREFS

Cf. A074997, A061715, A074460.

Sequence in context: A109290 A130441 A068570 * A061715 A280469 A072570

Adjacent sequences:  A074995 A074996 A074997 * A074999 A075000 A075001

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Aug 21 2002

EXTENSIONS

More terms from Sascha Kurz, Aug 22 2002

STATUS

approved

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Last modified October 16 20:55 EDT 2019. Contains 328103 sequences. (Running on oeis4.)