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 A247895 Least integer k > 0 such that prime(k) - k*n is prime. 3
 3, 7, 13, 31, 69, 190, 444, 1052, 2702, 6455, 15928, 40073, 100370, 251707, 637321, 1617175, 4124448, 10553415, 27066978, 69709680, 179992909, 465769803, 1208198532, 3140421716, 8179002120, 21338685408, 55762149030, 145935689361, 382465573486, 1003652347100 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture: (i) a(n) exists for any n > 0. (ii) For each integer n > 2, there is a positive integer k with k*n - prime(k) prime. LINKS Giovanni Resta, Table of n, a(n) for n = 1..50 Zhi-Wei Sun, A new theorem on the prime-counting function, arXiv:1409.5685 [math.NT], 2014-2017. EXAMPLE a(1) = 3 since prime(3) - 3*1 = 5 - 3 = 2 is prime. MATHEMATICA Do[k=1; Label[aa]; If[Prime[k]>k*n&&PrimeQ[Prime[k]-k*n], Print[n, " ", k]; Goto[bb]]; k=k+1; Goto[aa]; Label[bb]; Continue, {n, 1, 22}] CROSSREFS Cf. A000040, A247278, A247793. Sequence in context: A220746 A110436 A126879 * A336688 A155128 A176589 Adjacent sequences: A247892 A247893 A247894 * A247896 A247897 A247898 KEYWORD nonn AUTHOR Zhi-Wei Sun, Sep 28 2014 EXTENSIONS Terms a(23) and beyond from Giovanni Resta, Apr 22 2020 STATUS approved

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Last modified March 26 23:26 EDT 2023. Contains 361553 sequences. (Running on oeis4.)