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A363292 Numbers whose sum of (distinct) prime divisors (A008472) equals 7. 1
7, 10, 20, 40, 49, 50, 80, 100, 160, 200, 250, 320, 343, 400, 500, 640, 800, 1000, 1250, 1280, 1600, 2000, 2401, 2500, 2560, 3200, 4000, 5000, 5120, 6250, 6400, 8000, 10000, 10240, 12500, 12800, 16000, 16807, 20000, 20480, 25000, 25600, 31250, 32000, 40000, 40960 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
Union of A000420 = {7^k ; k > 0} and A033846 = {2^j*5^k ; j, k > 0}.
Sum_{n>=1} 1/a(n) = 5/12. - Amiram Eldar, Jul 27 2023
MATHEMATICA
seq[max_] := Union[Join[7^Range[Floor[Log[7, max]]], Flatten@ Table[2^i*5^j, {i, 1, Log2[max]}, {j, 1, Log[5, max/2^i]}]]]; seq[40000] (* Amiram Eldar, Jul 27 2023 *)
PROG
(PARI) select( {is_A363292(n)=vecsum(factor(n, 0)[, 1])==7}, [1..13^4]) \\ alternatively: [n | n<-[1..13^4], A008472(n)==7]
CROSSREFS
Cf. A008472 (sopf), A000420 (7^n), A033846 (2^m*5^n), A362948 (A008472 = 5).
Sequence in context: A064210 A249942 A300021 * A327977 A097634 A120312
KEYWORD
nonn,easy
AUTHOR
M. F. Hasler, Jul 20 2023
STATUS
approved

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Last modified July 16 05:19 EDT 2024. Contains 374343 sequences. (Running on oeis4.)