|
Search: id:A135777
|
|
|
| A135777 |
|
Numbers having number of divisors equal to number of digits in base 7. |
|
+0
1
|
|
| 1, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 49, 121, 169, 289, 343, 346, 355, 358, 362, 365, 371, 377, 381, 382, 386, 391, 393, 394, 395, 398, 403, 407, 411, 413, 415, 417, 422, 427, 437, 445, 446, 447, 451, 453, 454, 458, 466, 469, 471, 473, 478, 481
(list; graph; listen)
|
|
|
OFFSET
|
1,2
|
|
|
COMMENT
|
Since 7 is a prime, any power 7^k has k+1 divisors { 7^i ; i=0..k } and the same number of digits in base 7; thus the sequence A000420(k)=7^k is a subsequence of this one.
|
|
EXAMPLE
|
a(1) = 1 since 1 has 1 divisor and 1 digit (in base 7 as in any other base).
All other numbers have at least 2 divisors so there are no other members of the sequence below a(2) = 7 = 10[7] having 2 divisors { 1, 7 } and 2 digits in base 7.
|
|
PROGRAM
|
(PARI) for(d=1, 4, for(n=7^(d-1), 7^d-1, d==numdiv(n)&print1(n", ")))
|
|
CROSSREFS
|
Cf. A135772-A135779, A095862.
Sequence in context: A161850 A007775 A070884 this_sequence A090459 A090417 A020631
Adjacent sequences: A135774 A135775 A135776 this_sequence A135778 A135779 A135780
|
|
KEYWORD
|
base,nonn
|
|
AUTHOR
|
M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Nov 28 2007
|
|
|
Search completed in 0.002 seconds
|
