|
%I #10 Jan 29 2024 13:14:01
%S 1,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97
%N Noncomposite numbers n such that number of decimal digits of n = number of divisors of n.
%C Only 1 and primes with 2 decimal digits are here, so the sequence is finite: it consists of 1+25-4=22 terms. Part of A008364. Consists of the terms below 100 from A095862.
%t {u=1, ta=Table[0, {25}]}; Do[s=Apply[Plus, IntegerDigits[n]];s1=Length[IntegerDigits[n]]; If[Equal[s1, DivisorSigma[0, n]], Print[n];ta[[u]]=n;u=u+1], {n, 1, 100}]
%t Select[Range[100],!CompositeQ[#]&&DivisorSigma[0,#]==IntegerLength[#]&] (* _Harvey P. Dale_, Jan 29 2024 *)
%o (PARI) print1(1);forprime(p=9,99,print1(", "p)) \\ _Charles R Greathouse IV_, Apr 27, 2011
%Y Cf. A008364, A095862.
%K base,fini,full,nonn,easy
%O 1,2
%A _Labos Elemer_, Jun 25 2004
|
