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A106130 Numbers k such that k-th semiprime == 5 (mod k). 1
1, 60, 67, 68, 6919, 613380, 613426, 613558, 613596, 58155532, 58155539, 58155541, 58155542, 58155544 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The terms 60, 67, and 68 are numbers k such that the k-th semiprime is 3k+5; at k=6919, the k-th semiprime is 4k+5; at k = 613380, 613426, 613558, and 613596, the k-th semiprime is 5k+5; and at k = 58155532, 58155539, 58155541, 58155542, and 58155544, the k-th semiprime is 6k+5. No more terms should be expected up to through at least k = 6*10^9, where the ratio (k-th semiprime)/k is approaching 7. - Jon E. Schoenfield, Dec 17 2017

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

60 is a term because the 60th semiprime (i.e., 185) == 5 (mod 60).

PROG

(MuPAD) order := 0; for n from 1 to 10^100 do if numlib::Omega(n) = 2 then order := order+1; if n mod order = 5 then print(order); end_if; end_if; end_for; // Stefan Steinerberger, Nov 10 2005

CROSSREFS

Cf. A001358.

Sequence in context: A066722 A080862 A239415 * A216828 A131564 A036457

Adjacent sequences:  A106127 A106128 A106129 * A106131 A106132 A106133

KEYWORD

nonn,hard,more

AUTHOR

Shyam Sunder Gupta, May 07 2005

EXTENSIONS

More terms from Stefan Steinerberger, Nov 10 2005

a(9)-a(13) from Donovan Johnson, Oct 29 2008

Initial 1 added by Robert Israel, Dec 19 2017

STATUS

approved

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Last modified August 14 01:55 EDT 2020. Contains 336476 sequences. (Running on oeis4.)