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A001101
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Moran numbers: k such that k/(sum of digits of k) is prime.
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21
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18, 21, 27, 42, 45, 63, 84, 111, 114, 117, 133, 152, 153, 156, 171, 190, 195, 198, 201, 207, 209, 222, 228, 247, 261, 266, 285, 333, 370, 372, 399, 402, 407, 423, 444, 465, 481, 511, 516, 518, 531, 555, 558, 592, 603
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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REFERENCES
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Bill Moran, Problem 2074: The Moran Numbers, J. Rec. Math., Vol. 25 No. 3, pp. 215, 1993.
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LINKS
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MATHEMATICA
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PROG
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(Haskell)
import Data.List (findIndices)
a001101 n = a001101_list !! (n-1)
a001101_list = map succ $ findIndices p [1..] where
p n = m == 0 && a010051 n' == 1 where
(n', m) = divMod n (a007953 n)
(Python)
# 1000000 primes: https://primes.utm.edu/lists/small/millions/primes1.zip
# "primes1.txt" must be formatted as a b-file before execution
import csv
with open("primes1.txt", "r") as f:
....reader = csv.reader(f, delimiter=" ")
....primes = set([int(rows[1]) for rows in reader])
i, n = 1, 1
with open("b001101.txt", "w") as f:
....while i <= 10000:
........if n % sum(map(int, str(n))) == 0 and n/sum(map(int, str(n))) in primes:
............f.write("{} {}\n".format(i, n))
............i += 1
........n += 1
(Python)
from sympy import isprime
def ok(n): s = sum(map(int, str(n))); return s and n%s==0 and isprime(n//s)
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CROSSREFS
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Subsequence of A005349, Niven (or Harshad) numbers.
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KEYWORD
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nonn,base,nice
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AUTHOR
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Bill Moran (moran1(AT)llnl.gov)
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EXTENSIONS
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STATUS
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approved
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