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A100411
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Numbers n such that n is the phi(n)-th nonprime number.
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1
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1, 4, 8, 27, 35, 215, 235, 2611, 65113, 174647, 1301317, 1302509, 5021647, 10885081, 36319939, 70112131, 70113559, 325575773, 514258883, 742327529, 1069238453, 18721771909, 27788563039
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| n is in the sequence iff n is't prime and n=phi(n)+pi(n). This sequence is a subsequence of A037170 and 2 is the only term of A037170 which is not in this sequence because 2 is the only prime p such that p=phi(p)+pi(p).
There is no further term up to 10^9. [From Farideh Firoozbakht (mymontain(AT)yahoo.com), Jul 26 2009]
a(24) > 10^11. [From Donovan Johnson (donovan.johnson(AT)yahoo.com), Feb 05 2010]
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EXAMPLE
| 27 is in the sequence because phi(27)=18 and 27 is the 18-th nonprime number, the first 17 nonprime numbers are 1,4,6,8,9,10,12,14,15,16,18,20,21,22,24,25 & 26.
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CROSSREFS
| Cf. A037170, A100410, A018252.
Sequence in context: A126733 A012982 A012952 * A065405 A026085 A036720
Adjacent sequences: A100408 A100409 A100410 * A100412 A100413 A100414
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KEYWORD
| more,nonn
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AUTHOR
| Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 01 2004
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EXTENSIONS
| a(19)-a(20) from Farideh Firoozbakht (mymontain(AT)yahoo.com), Jul 26 2009
a(21)-a(23) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Feb 05 2010
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