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 A278242 Least number with the prime signature of 2^n + 1. 3
 2, 2, 2, 4, 2, 6, 6, 6, 2, 24, 12, 6, 6, 6, 30, 60, 2, 6, 210, 6, 6, 60, 30, 6, 30, 210, 210, 240, 6, 30, 4620, 6, 6, 420, 210, 2310, 210, 30, 210, 60, 6, 30, 30030, 6, 30, 9240, 2310, 30, 30, 30, 9240, 4620, 30, 30, 30030, 4620, 30, 420, 30, 210, 210, 6, 2310, 9240, 6, 30030, 30030, 30, 60, 420, 60060, 30, 2310, 30, 2310, 60060, 210, 30030, 446185740, 6, 30 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Antti Karttunen, Table of n, a(n) for n = 0..257 FORMULA a(n) = A046523(A000051(n)). MATHEMATICA Table[Times @@ MapIndexed[(Prime@ First@ #2)^#1 &, #] &@ If[Length@ # == 1 && #[[1, 1]] == 1, {0}, Reverse@ Sort@ #[[All, -1]] &@ FactorInteger[ 2^n + 1], {n, 77}] (* Michael De Vlieger, Nov 21 2016 *) PROG (PARI) A046523(n) = my(f=vecsort(factor(n)[, 2], , 4), p); prod(i=1, #f, (p=nextprime(p+1))^f[i]) \\ from Charles R Greathouse IV, Aug 17 2011 A278242(n) = A046523((2^n)+1); for(n=0, 257, write("b278242.txt", n, " ", A278242(n))); (Scheme) (define (A278242 n) (A046523 (A000051 n))) CROSSREFS Cf. A000051, A046523. Cf. A073936 (positions of 6's), A092559 (positions of 4's and 6's). Cf. also A278240. Sequence in context: A345067 A066243 A366606 * A035580 A135293 A216951 Adjacent sequences: A278239 A278240 A278241 * A278243 A278244 A278245 KEYWORD nonn AUTHOR Antti Karttunen, Nov 19 2016 STATUS approved

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Last modified August 13 05:48 EDT 2024. Contains 375113 sequences. (Running on oeis4.)