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 A220218 Numbers where all exponents in its prime factorization are one less than a prime. 3
 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 25, 26, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 55, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 80 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sequence has positive density, between 0.83 and 0.89; probably about 0.87951. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 P. ErdÅ‘s and L. Mirsky, The distribution of values of the divisor function d(n), Proc. London Math. Soc. 2 (1952), pp. 257-271. MATHEMATICA Select[Range[100], AllTrue[Transpose[FactorInteger[#]][[2]]+1, PrimeQ]&] (* Harvey P. Dale, Sep 29 2014 *) PROG (PARI) is(n)=vecmin(apply(n->isprime(n+1), factor(max(n, 2))[, 2])) \\ Charles R Greathouse IV, Dec 07 2012 (Haskell) a220218 n = a220218_list !! (n-1) a220218_list = 1 : filter                (all (== 1) . map (a010051' . (+ 1)) . a124010_row) [1..] -- Reinhard Zumkeller, Nov 30 2015 CROSSREFS Apart from the first term, a subsequence of A096432. Cf. A010051, A124010. Sequence in context: A219227 A007412 A270420 * A096432 A138302 A270428 Adjacent sequences:  A220215 A220216 A220217 * A220219 A220220 A220221 KEYWORD nonn AUTHOR Charles R Greathouse IV, Dec 07 2012 STATUS approved

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Last modified January 22 23:00 EST 2019. Contains 319365 sequences. (Running on oeis4.)