|
Search: id:A156208
|
|
|
| A156208 |
|
Numbers n such that the sum of of the products of the digits and their position m in n is prime. |
|
+0
1
|
|
| 2, 3, 5, 7, 3, 5, 7, 11, 13, 17, 19, 2, 3, 5, 7, 11, 13, 17, 19, 5, 7, 11, 13, 17, 19, 23, 7, 11, 13, 17, 19, 23, 11, 13, 17, 19, 23, 7, 13, 19, 3, 5, 11, 17, 23, 29, 7, 13, 19, 31, 11, 17, 23, 29, 13, 19, 31, 37, 17, 23, 29, 41, 19, 31, 37, 43, 2, 5, 11, 17, 23, 29, 7, 13, 19, 31, 11
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
FORMULA
|
Given a number n with digits d1d2d3...dm, a(n) = d1*1+d2*2+d3*3+...+dm*m.
If a(n) is prime, list it.
|
|
EXAMPLE
|
For n=19 we have 1*1 + 2*9 = 19 prime and the sequence.
|
|
PROGRAM
|
(PARI) g1(n) = for(j=1, n, if(isprime(g(j)), print1(g(j)", ")))
g(n) = v=Vec((Str(n))); sum(x=1, length(v), x*eval(v[x]))
|
|
CROSSREFS
|
Sequence in context: A143950 A108534 A039706 this_sequence A073034 A126050 A163821
Adjacent sequences: A156205 A156206 A156207 this_sequence A156209 A156210 A156211
|
|
KEYWORD
|
base,nonn
|
|
AUTHOR
|
Cino Hilliard (hillcino368(AT)hotmail.com), Feb 05 2009, Feb 08 2009
|
|
|
Search completed in 0.002 seconds
|
