A235108 - OEIS

A235108

Semiprimes with digits in strictly decreasing order.

4, 6, 9, 10, 21, 51, 62, 65, 74, 82, 85, 86, 87, 91, 93, 94, 95, 321, 542, 543, 721, 731, 753, 763, 831, 841, 842, 843, 851, 862, 865, 871, 921, 943, 951, 961, 965, 973, 974, 982, 985, 4321, 5321, 6431, 6541, 6542, 7421, 7431, 7531, 7543, 7631, 7642, 7651

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..159 (complete sequence)

MAPLE

b:= proc(n) n, seq(b(10*n+j), j=irem(n, 10)-1..0, -1) end:

select(numtheory[bigomega]=2, {seq(b(n), n=1..9)})[]; # Alois P. Heinz, Apr 13 2025

MATHEMATICA

Select[Range[10000], PrimeOmega[#]==2&&Max[Differences[IntegerDigits[#]]]<0&] (* Harvey P. Dale, Aug 18 2024 *)

PROG

(PARI)

list(lim)=my(v=List(), t); forprime(p=2, sqrt(lim), t=p; forprime(q=p, lim\t, listput(v, t*q))); vecsort(Vec(v)) \\ From A001358

isdecr(a) = {my(b=-1); until(a==0, if(a%10<=b, return(0)); b=a%10; a\=10); return(1)}

u=list(50000); s=[]; for(n=1, #u, if(isdecr(u[n]), s=concat(s, u[n]))); s

CROSSREFS

Cf. A001358, A108635, A108634, A135355.

Sequence in context: A135257 A118697 A118695 * A215478 A118693 A084668

Adjacent sequences: A235105 A235106 A235107 * A235109 A235110 A235111

KEYWORD

nonn,base,fini,full

AUTHOR

Colin Barker, Jan 03 2014

STATUS

approved