A109029 9-almost primes (A046312) whose digit reversal is different and also has 9 prime factors (with multiplicity). "Emirp Tsomla-9.".

21168, 23424, 23616, 27456, 41184, 42432, 48114, 61632, 65472, 86112, 211410, 212256, 213192, 215232, 217440, 219072, 230208, 232512, 236925, 236928, 238656, 238680, 251100, 251505, 251748, 253824, 255024, 255960, 257856, 259968, 270912

Offset

1,1

Comments

This sequence is the k = 8 instance of the series which begins with k = 1 (emirps), k = 2 (emirpimes), k = 3 (emirp tsomla-3 = A109023), k = 4 (emirp tsomla-4 = A109024), k = 5 (emirp tsomla-5 = A109025), k = 6 (emirp tsomla-6 = A109026), k = 7 (emirp tsomla-7 = A109027), k = 8 (emirp tsomla-8 = A109028).

The Mathematica code for this was written by Ray Chandler who extended this sequence. He also has more values.

References

Jonathan Vos Post, "1066 and All That: Emirp Tsomla-3 and Related Integer Sequences." Forthcoming paper on this sequence.

Links

Table of n, a(n) for n=1..31.

Eric Weisstein's World of Mathematics, Almost Prime.

Eric Weisstein's World of Mathematics, Emirp.

Eric Weisstein and Jonathan Vos Post, Emirpimes.

Example

a(1) = 21168 is in this sequence because 21168 = 2^4 * 3^3 * 7^2 is a 9-almost prime and reverse(21168) = 86112 = 2^5 * 3^2 * 13 * 23 is also a 9-almost prime.

Mathematica

okQ[n_]:=Module[{idn=IntegerDigits[n], ridn}, ridn=Reverse[idn]; idn!=ridn && PrimeOmega[n]==9&&PrimeOmega[FromDigits[ridn]]==9]; Select[Range[ 271000], okQ] (* Harvey P. Dale, Sep 24 2011 *)

Crossrefs

Cf. A046312, A006567, A097393, A109018, A109023-A109028, A109030-A109131.

Sequence in context: A294059 A255949 A273659 * A284915 A252165 A289674

Adjacent sequences: A109026 A109027 A109028 * A109030 A109031 A109032

Keyword

nonn,base

Author

Jonathan Vos Post, Jun 16 2005

Status

approved