OFFSET
1,2
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
FORMULA
MATHEMATICA
Array[IntegerDigits[# (# + 1) / 2][[1]]&, 100] (* Vincenzo Librandi, Apr 12 2019 *)
IntegerDigits[#][[1]]&/@Accumulate[Range[100]] (* Harvey P. Dale, Oct 15 2022 *)
PROG
(PARI) a(n) = digits(n*(n+1)/2)[1]; \\ Michel Marcus, Jun 20 2018
(Magma) [Intseq((n*(n+1) div 2))[#Intseq((n*(n+1) div 2))]: n in [1..100]]; // Vincenzo Librandi, Apr 12 2019
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
STATUS
approved