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A278253
Least number with the prime signature of the n-th triangular number.
10
1, 2, 6, 6, 6, 6, 12, 36, 12, 6, 30, 30, 6, 30, 120, 24, 12, 12, 30, 210, 30, 6, 60, 180, 12, 24, 120, 30, 30, 30, 48, 240, 30, 30, 420, 60, 6, 30, 420, 60, 30, 30, 30, 420, 60, 6, 120, 360, 36, 60, 210, 30, 24, 120, 420, 420, 30, 6, 210, 210, 6, 60, 1440, 480, 210, 30, 30, 210, 210, 30, 180, 180, 6, 60, 420, 210, 210, 30, 120, 2160, 48, 6, 210, 2310, 30, 30
OFFSET
1,2
LINKS
FORMULA
a(n) = A046523(A000217(n)).
MATHEMATICA
Table[Times @@ MapIndexed[(Prime@ First@ #2)^#1 &, #] &@ If[Length@ # == 1 && #[[1, 1]] == 1, {0}, Reverse@ Sort@ #[[All, -1]]] &@ FactorInteger[ (n^2 - n)/2], {n, 2, 87}] (* Michael De Vlieger, Nov 21 2016 *)
PROG
(Scheme) (define (A278253 n) (A046523 (A000217 n)))
(PARI) a(n)=my(f=vecsort(factor(n*(n+1)/2)[, 2], , 4), p); prod(i=1, #f, (p=nextprime(p+1))^f[i]) \\ Charles R Greathouse IV, Feb 03 2017
CROSSREFS
Diagonal 2 of triangle A278218.
Sequence in context: A304363 A247097 A258576 * A294961 A048765 A103643
KEYWORD
nonn
AUTHOR
Antti Karttunen, Nov 19 2016
STATUS
approved