A246569 Semiprimes with strictly increasing product of digits.

4, 6, 9, 25, 26, 35, 38, 39, 49, 58, 69, 87, 249, 259, 278, 289, 299, 398, 478, 489, 579, 589, 679, 689, 699, 789, 799, 889, 899, 2589, 2599, 2779, 2798, 2899, 3799, 3898, 3899, 4798, 4979, 4989, 5799, 5899, 5999, 6989, 6999, 7899, 7999, 8899, 9899, 19999, 26799

Offset

1,1

Comments

Primes of this form are at A230041.

Links

K. D. Bajpai, Table of n, a(n) for n = 1..169

Example

a(6) = 35 = 5 * 7, which is semiprime. Product of its digits = 3 * 5 = 15.
a(7) = 38 = 2 * 19, which is semiprime. Product of its digits = 3 * 8 = 24.
Since 24 > 15, 35 and 38 appear in the sequence.

Mathematica

A246569 = { }; t = 0; Do[s = Apply[Times, IntegerDigits[k]]; If[PrimeOmega[k] == 2 && s > t, t = s; AppendTo[A246569, k]], {k, 1, 30000}]; A246569

Crossrefs

Cf. A001358, A230041.

Sequence in context: A229129 A272436 A338309 * A368648 A326063 A085721

Adjacent sequences: A246566 A246567 A246568 * A246570 A246571 A246572

Keyword

nonn,base

Author

K. D. Bajpai, Aug 30 2014

Status

approved