id:A039736 - OEIS Search Results

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a(n) = number of primes q<p having (p mod q) = 2, where p = n-th prime.

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0, 0, 1, 1, 1, 1, 2, 1, 2, 1, 1, 2, 2, 1, 2, 2, 2, 1, 2, 2, 1, 2, 1, 2, 2, 2, 1, 3, 1, 2, 1, 2, 2, 1, 2, 1, 2, 2, 3, 2, 2, 1, 2, 1, 3, 1, 2, 2, 2, 1, 3, 2, 1, 2, 3, 2, 2, 1, 2, 2, 1, 2, 2, 2, 1, 3, 2, 2, 3, 1, 2, 3, 2, 2, 2, 2, 2, 2, 3, 2, 2, 1, 3, 1, 2, 2, 2, 3, 2, 1, 3, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 3, 3, 2, 1 (list; graph; listen)

	OFFSET	`1,7`
	COMMENT	`Number of distinct prime factors of p_n-2.`
	EXAMPLE	`First prime is 2, p_1-2 = 0 which has no prime factors, 2nd is 3, 3-2 = 1 which also has no prime factors. p_6 is 17 and 15 has 2 distinct prime divisors. a(219) = A001221(Prime(219)-2) = A001221(1365) = A001221(357*13) = 4`
	MATHEMATICA	`Length[ FactorInteger[ Prime[ n ]-2 ] ]`
	CROSSREFS	`Cf. A001221.` `Sequence in context: A094840 A035218 A139355 this_sequence A093921 A140192 A065373` `Adjacent sequences: A039733 A039734 A039735 this_sequence A039737 A039738 A039739`
	KEYWORD	`nonn`
	AUTHOR	`Clark Kimberling (ck6(AT)evansville.edu)`
	EXTENSIONS	`More terms from Labos E. (labos(AT)ana.sote.hu)`

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Last modified November 23 17:09 EST 2009. Contains 167438 sequences.

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