OFFSET
1,1
COMMENTS
A prime index of n is a number m such that prime(m) divides n.
If n is in the sequence, then so are all multiples of n. - Robert Israel, Mar 19 2019
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
The sequence of terms together with their prime indices begins:
2: {1}
4: {1,1}
6: {1,2}
8: {1,1,1}
10: {1,3}
12: {1,1,2}
14: {1,4}
15: {2,3}
16: {1,1,1,1}
18: {1,2,2}
20: {1,1,3}
22: {1,5}
24: {1,1,1,2}
26: {1,6}
28: {1,1,4}
30: {1,2,3}
32: {1,1,1,1,1}
34: {1,7}
36: {1,1,2,2}
MAPLE
filter:= proc(n) local F;
F:= map(numtheory:-pi, numtheory:-factorset(n));
ormap(t -> n mod t = 0, F);
end proc:
select(filter, [$1..200]); # Robert Israel, Mar 19 2019
MATHEMATICA
Select[Range[100], Or@@Cases[If[#==1, {}, FactorInteger[#]], {p_, _}:>Divisible[#, PrimePi[p]]]&]
PROG
(PARI) isok(n) = {my(f = factor(n)[, 1]); for (k=1, #f, if (!(n % primepi(f[k])), return (1)); ); return (0); } \\ Michel Marcus, Mar 19 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Mar 18 2019
STATUS
approved