A357173 - OEIS

%I #20 Sep 18 2022 10:21:11

%S 1,2,4,6,12,24,36,48,72,144,336,468,504,936,1008,1512,2520,3024,5040,

%T 6552,7560,13104,19656,39312,78624,98280,196560,393120,668304,1244880,

%U 1670760,1867320,3341520,3734640,7469280,22407840,26142480,31744440,52284960,63488880

%N Positions of records in A357171, i.e., integers whose number of divisors whose decimal digits are in strictly increasing order sets a new record.

%C As A009993 is finite, this sequence is necessarily finite.

%C Corresponding records are 1, 2, 3, 4, 6, 8, 9, 10, 11, ...

%e a(6) = 24 is in the sequence because A357171(24) = 8 is larger than any earlier value in A357171.

%t s[n_] := DivisorSum[n, 1 &, Less @@ IntegerDigits[#] &]; seq = {}; sm = 0; Do[If[(sn = s[n]) > sm, sm = sn; AppendTo[seq, n]], {n, 1, 10^4}]; seq (* _Amiram Eldar_, Sep 17 2022 *)

%o (PARI) isok(d) = Set(d=digits(d)) == d; \\ A009993

%o f(n) = sumdiv(n, d, isok(d)); \\ A357171

%o lista(nn) = my(r=0, list = List()); for (k=1, nn, my(m=f(k)); if (m>r, listput(list, k); r = m);); Vec(list); \\ _Michel Marcus_, Sep 18 2022

%Y Cf. A009993, A357171, A357172, A160218.

%Y Similar sequences: A093036, A340548, A355595.

%K nonn,base,fini

%O 1,2

%A _Bernard Schott_, Sep 17 2022

%E More terms from _Amiram Eldar_, Sep 17 2022