A108634 -id:A108634 - cp's OEIS frontend

A108635 Semiprimes with property that digits are in nonincreasing order.

4, 6, 9, 10, 21, 22, 33, 51, 55, 62, 65, 74, 77, 82, 85, 86, 87, 91, 93, 94, 95, 111, 221, 321, 411, 422, 511, 533, 542, 543, 551, 553, 554, 611, 622, 633, 655, 662, 721, 731, 753, 755, 763, 766, 771, 831, 841, 842, 843, 851, 862, 865, 866, 871, 886, 921, 922

Offset: 1

Zak Seidov, Jun 14 2005

			The semiprime 14 is missing because 4 > 1.

Cf. A108634.

Select[Range[1000], Plus@@Last/@FactorInteger[ # ]\[Equal]2&&OrderedQ[Reverse[IntegerDigits[ # ]]]&]

A235108 Semiprimes with digits in strictly decreasing order.

Original entry on oeis.org

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

Offset: 1

Colin Barker, Jan 03 2014

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

Cf. A001358, A108635, A108634, A135355.

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

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

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

cp's OEIS Frontend

A108635 Semiprimes with property that digits are in nonincreasing order.

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