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A095862
Numbers whose number of decimal digits and number of divisors are equal.
12
1, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 121, 169, 289, 361, 529, 841, 961, 1003, 1006, 1007, 1011, 1018, 1027, 1037, 1041, 1042, 1043, 1046, 1047, 1055, 1057, 1059, 1067, 1073, 1077, 1079, 1081, 1082, 1094, 1099
OFFSET
1,2
COMMENTS
An element of this sequence is prime iff it has 2 digits, which is the case for a(2)=11 through a(22); sequence A096489 lists exactly these and the leading term a(1)=1 (the only noncomposite number which is not prime). - M. F. Hasler, Nov 29 2007
LINKS
MAPLE
q:= n-> is(length(n)=numtheory[tau](n)):
select(q, [$1..1100])[]; # Alois P. Heinz, Jun 18 2021
MATHEMATICA
Select[Range[1100], IntegerLength[#]==DivisorSigma[0, #]&] (* Harvey P. Dale, Oct 19 2015 *)
CROSSREFS
Cf. A096489 (= a(1)..a(22) = noncomposite elements of this sequence).
Cf. A135772-A135779 (analog for bases 2...9).
Sequence in context: A120533 A226108 A273906 * A125845 A108871 A347819
KEYWORD
base,nonn
AUTHOR
Ray Chandler, Jun 28 2004
EXTENSIONS
Edited by M. F. Hasler, Nov 29 2007
STATUS
approved