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A278165 Least number with the prime signature of the n-th Jacobsthal number. 5
1, 1, 2, 2, 2, 6, 2, 6, 12, 6, 2, 210, 2, 6, 30, 30, 2, 420, 2, 420, 30, 30, 2, 30030, 30, 6, 120, 2310, 6, 30030, 2, 210, 210, 6, 210, 19399380, 6, 6, 30, 60060, 6, 60060, 2, 30030, 4620, 30, 6, 223092870, 6, 30030, 2310, 30030, 6, 120120, 420, 510510, 210, 2310, 30, 401120980260, 2, 6, 4620, 30030, 2310, 9699690, 6, 30030, 210, 9699690, 6, 14841476269620, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Antti Karttunen (terms 1..257) & Hans Havermann, Table of n, a(n) for n = 1..1032

FORMULA

a(n) = A046523(A001045(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)/3], {n, 120}] (* Michael De Vlieger, Nov 21 2016 *)

PROG

(PARI)

A001045(n) = (2^n - (-1)^n) / 3;

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

A278165(n) = A046523(A001045(n));

for(n=1, 257, write("b278165.txt", n, " ", A278165(n)));

(Scheme) (define (A278165 n) (A046523 (A001045 n)))

CROSSREFS

Cf. A001045, A046523.

Cf. A107036 (positions of 2's), A286565 (rgs-version of this sequence).

Cf. also A278245, A278248, A278258, A286567.

Sequence in context: A291439 A023957 A224964 * A074928 A285713 A278230

Adjacent sequences:  A278162 A278163 A278164 * A278166 A278167 A278168

KEYWORD

nonn

AUTHOR

Antti Karttunen, Nov 19 2016

STATUS

approved

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Last modified August 22 02:44 EDT 2019. Contains 326169 sequences. (Running on oeis4.)