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A167759 Numbers n such that d(n)=isolated number. 2
2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 26, 27, 28, 29, 31, 32, 33, 34, 35, 37, 38, 39, 41, 43, 44, 45, 46, 47, 50, 51, 52, 53, 55, 57, 58, 59, 60, 61, 62, 63, 65, 67, 68, 69, 71, 72, 73, 74, 75, 76, 77, 79, 82, 83, 84, 85, 86, 87, 89, 90, 91, 92 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Where 2, 4, 6, 12, 18, 23, 30, 37,.. are isolated numbers A167706. The isolated numbers of divisors of n. Numbers n such that number of divisors of n is isolated number. Also, the positions of isolated numbers in A000005.

LINKS

Table of n, a(n) for n=1..71.

FORMULA

A000005(a(n))=isolated number.

EXAMPLE

A000005(a(1)=2)=2; A000005(a(2)=3)=2; A000005(a(3)=5)=2; A000005(a(4)=6)=4.

MAPLE

isA007510 := proc(n) if isprime(n) then not isprime(n+2) and not isprime(n-2) ; else false; end if; end proc: isA014574 := proc(n) isprime(n+1) and isprime(n-1) ; end proc: isA167706 := proc(n) isA007510(n) or isA014574(n) ; end proc: isA167759 := proc(n) isA167706(numtheory[tau](n)) ; end proc: for n from 1 to 100 do if isA167759(n) then printf("%d, ", n) ; fi; od: [From R. J. Mathar, Nov 16 2009]

CROSSREFS

Cf. A000005, A002035, A167706.

Sequence in context: A028809 A028785 A166546 * A028812 A039251 A283296

Adjacent sequences:  A167756 A167757 A167758 * A167760 A167761 A167762

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Nov 11 2009

STATUS

approved

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Last modified October 17 09:00 EDT 2018. Contains 316276 sequences. (Running on oeis4.)