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

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

Offset

1,1

Comments

The average of twin primes is a member.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

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: A249630 A109290 A130441 * A061715 A280469 A353073

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

Offset corrected by Amiram Eldar, Jan 02 2020

Status

approved