A096489 Noncomposite numbers n such that number of decimal digits of n = number of divisors of n.

1, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97

Offset

1,2

Comments

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.

Links

Table of n, a(n) for n=1..22.

Mathematica

{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}]
Select[Range[100], !CompositeQ[#]&&DivisorSigma[0, #]==IntegerLength[#]&] (* Harvey P. Dale, Jan 29 2024 *)

Prog

(PARI) print1(1); forprime(p=9, 99, print1(", "p)) \\ Charles R Greathouse IV, Apr 27, 2011

Crossrefs

Cf. A008364, A095862.

Sequence in context: A063193 A056758 A322273 * A008364 A140461 A120533

Adjacent sequences: A096486 A096487 A096488 * A096490 A096491 A096492

Keyword

base,fini,full,nonn,easy

Author

Labos Elemer, Jun 25 2004

Status

approved