id:A082650 - OEIS Search Results

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Number of primes < n of form 1+k*spf(n), where spf(n) is the smallest prime factor of n (A020639).

+0
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0, 0, 0, 1, 0, 2, 0, 3, 1, 3, 0, 4, 0, 5, 2, 5, 0, 6, 0, 7, 3, 7, 0, 8, 1, 8, 3, 8, 0, 9, 0, 10, 4, 10, 2, 10, 0, 11, 5, 11, 0, 12, 0, 13, 6, 13, 0, 14, 2, 14, 6, 14, 0, 15, 3, 15, 6, 15, 0, 16, 0, 17, 7, 17, 4, 17, 0, 18, 8, 18, 0, 19, 0, 20, 9, 20, 3, 20, 0, 21, 10, 21, 0, 22, 5, 22, 10, 22, 0 (list; graph; listen)

	OFFSET	`1,6`
	LINKS	`Index entries for sequences related to primes in arithmetic progressions`
	FORMULA	`a(2n)=A000720(2n)-1; a(n)=0 iff n=1 or n prime, a(A008578(n))=1. - Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com), Sep 11 2003`
	EXAMPLE	`n=20, spf(20)=2: 8 primes of form 1+k2: 1+12=3, 1+22=5,` `1+32=7, 1+52=11, 1+62=13, 1+82=17, and 1+92=19, therefore a(20)=8;` `n=21, spf(21)=3: 3 primes of form 1+k3: 1+23=7, 1+43=13, and` `1+63=19, therefore a(21)=3.`
	CROSSREFS	`Cf. A035096.` `Sequence in context: A071504 A125943 A098006 this_sequence A015710 A054875 A029239` `Adjacent sequences: A082647 A082648 A082649 this_sequence A082651 A082652 A082653`
	KEYWORD	`nonn`
	AUTHOR	`Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com), May 16 2003`

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Last modified August 19 23:53 EDT 2008. Contains 142930 sequences.

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