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A085647
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Semiprimes whose prime factors p*q have an equal number of decimal digits and p is not equal to q.
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2
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6, 10, 14, 15, 21, 35, 143, 187, 209, 221, 247, 253, 299, 319, 323, 341, 377, 391, 403, 407, 437, 451, 473, 481, 493, 517, 527, 533, 551, 559, 583, 589, 611, 629, 649, 667, 671, 689, 697, 703, 713, 731, 737, 767, 779, 781, 793, 799, 803, 817, 851, 869, 871
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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Chai Wah Wu, Table of n, a(n) for n = 1..10369
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MATHEMATICA
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spddQ[n_]:=Module[{fi=FactorInteger[n][[All, 1]]}, PrimeOmega[n]==2 && fi[[2]]- fi[[1]]>0&&IntegerLength[fi[[1]]]==IntegerLength[fi[[2]]]]; Select[Range[900], spddQ]//Quiet (* Harvey P. Dale, Jul 14 2021 *)
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PROG
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(Python)
from sympy import sieve
A085647 = []
for n in range(3):
....pr = list(sieve.primerange(10**n, 10**(n+1)))
....for i, p in enumerate(pr, start=1):
........for q in pr[i:]:
............A085647.append(p*q)
A085647 = sorted(A085647)
# Chai Wah Wu, Aug 26 2014
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CROSSREFS
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Cf. A001358, A078972.
Sequence in context: A225706 A063078 A064452 * A072901 A162409 A226494
Adjacent sequences: A085644 A085645 A085646 * A085648 A085649 A085650
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KEYWORD
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base,easy,nonn
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AUTHOR
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Amarnath Murthy, Jason Earls, Jul 11 2003
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STATUS
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approved
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