id:A072342 - OEIS Search Results

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a(n) = the least natural number k such that k*reverse(n) + 1 is prime.

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1, 1, 2, 1, 2, 1, 4, 2, 2, 1, 2, 2, 10, 2, 2, 6, 8, 2, 6, 1, 1, 1, 3, 1, 1, 5, 1, 1, 3, 2, 4, 2, 2, 4, 2, 2, 4, 2, 4, 1, 2, 3, 3, 2, 2, 3, 2, 4, 3, 2, 2, 4, 2, 4, 6, 2, 2, 12, 2, 1, 1, 2, 1, 1, 2, 1, 3, 2, 1, 4, 6, 4, 4, 6, 4, 4, 6, 4, 4, 2, 1, 1, 5, 2, 1, 2, 1, 1, 2, 2, 10, 2, 2, 4, 12, 2, 4, 2, 2, 1, 6, 8 (list; graph; listen)

	OFFSET	`1,3`
	COMMENT	`Conjecture: a(n) is less than or equal to n for all n.`
	EXAMPLE	`Reverse(12) = 21 and the least natural number k such that 21 k + 1 is prime is k = 2; so a(12) = 2.`
	MATHEMATICA	`f[n_] := Module[{i}, i = 0; While[ ! PrimeQ[i*FromDigits[Reverse[IntegerDigits[n]]]+ 1], i++ ]; i]; Table[f[i], {i, 1, 150}]`
	CROSSREFS	`Sequence in context: A100380 A080825 A034693 this_sequence A066389 A077191 A050363` `Adjacent sequences: A072339 A072340 A072341 this_sequence A072343 A072344 A072345`
	KEYWORD	`base,nonn`
	AUTHOR	`Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jul 16 2002`

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

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