|
| |
|
|
A079142
|
|
Numbers divisible by prime integer parts of their square roots.
|
|
0
| |
|
|
4, 6, 8, 9, 12, 15, 25, 30, 35, 49, 56, 63, 121, 132, 143, 169, 182, 195, 289, 306, 323, 361, 380, 399, 529, 552, 575, 841, 870, 899, 961, 992, 1023, 1369, 1406, 1443, 1681, 1722, 1763, 1849, 1892, 1935, 2209, 2256, 2303, 2809, 2862, 2915, 3481, 3540, 3599
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,1
|
|
|
COMMENTS
| n is in the sequence if r=floor(sqrt(n)) is prime and r divides n.
Union of the 3 sequences A001248={p^2}, A036690={p(p+1)} and {p(p+2)} for p prime.
The sum of the reciprocals = 1.04...
|
|
|
FORMULA
| a(n) = prime(floor(n/3+1))*(prime(floor(n/3+1)) + (n mod 3))
|
|
|
EXAMPLE
| 56 is in the sequence because floor(sqrt(56)) = 7 is prime and 7 divides 56.
|
|
|
MATHEMATICA
| Flatten[ #(#+{0, 1, 2})&/@Prime/@Range[20]]
a[n_] := (p=Prime[Floor[n/3+1]])(p+Mod[n, 3])
|
|
|
PROG
| (PARI) ipsqrt(n) = { sr= 0; for(x=1, n, v = floor(sqrt(x)); if(isprime(v) && x%v == 0, print1(x" "); sr+=1.0/x; ); ); print(); print(sr); } \\ numbers divisible by prime integer parts of their square roots.
|
|
|
CROSSREFS
| Sequence in context: A157942 A122786 A092630 * A062002 A028958 A200878
Adjacent sequences: A079139 A079140 A079141 * A079143 A079144 A079145
|
|
|
KEYWORD
| nonn
|
|
|
AUTHOR
| Cino Hilliard (hillcino368(AT)gmail.com), Dec 26 2002
|
| |
|
|
