A109023 3-almost primes (A014612) whose digit reversal is different and also has 3 prime factors (with multiplicity).

117, 147, 165, 244, 246, 285, 286, 290, 338, 366, 369, 406, 418, 425, 435, 438, 442, 475, 498, 506, 507, 508, 524, 534, 539, 548, 561, 574, 582, 604, 605, 609, 628, 642, 663, 670, 682, 705, 711, 741, 759, 805, 814, 826, 833, 834, 845, 890, 894, 906, 935

Offset

1,1

Comments

This sequence is the k = 3 instance of the series which begins with k = 1, k = 2.

References

W. W. R. Ball and H. S. M. Coxeter, Mathematical Recreations and Essays, 13th ed. New York: Dover, pp. 14-15, 1987.

J. Edalj, Problem 1622. L'Intermédiaire des Mathématiciens, 16, 34, 1909.

Links

David A. Corneth, Table of n, a(n) for n = 1..10000

J. Jonesco, Query 1622, L'Intermédiaire des Mathématiciens, 200, Tome VI, 1899.

Eric Weisstein's World of Mathematics, Almost Prime.

Eric Weisstein's World of Mathematics, Emirp.

Eric Weisstein and Jonathan Vos Post, Emirpimes.

Example

1066 is in this sequence because 1066 = 2 * 13 * 41, making it a 3-almost prime and reverse(1066) = 6601 = 7 * 23 * 41, also a 3-almost prime.
2001 is in this sequence because 2001 = 3 * 23 * 29 and reverse(2001) = 1002 = 2 * 3 * 167.

Mathematica

Select[Range[1000], PrimeOmega[#]==3&&PrimeOmega[FromDigits[Reverse[IntegerDigits[#]]]]==3&&!PalindromeQ[#]&] (* James C. McMahon, Mar 06 2024 *)

Prog

(PARI) is(n) = {
	my(r = fromdigits(Vecrev(digits(n))));
	n!=r && bigomega(n) == 3 && bigomega(r) == 3
} \\ David A. Corneth, Mar 07 2024

Crossrefs

Cf. A006567, A097393, A109018, A109024, A109025, A109026, A109027, A109028, A109029, A109030, A109031.

Sequence in context: A084344 A015706 A095625 * A272388 A272389 A201021

Adjacent sequences: A109020 A109021 A109022 * A109024 A109025 A109026

Keyword

nonn,base

Author

Jonathan Vos Post, Jun 16 2005

Extensions

1002 replaced by 935 - R. J. Mathar, Dec 14 2009

Status

approved