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 A078795 Concatenate first n triangular numbers. 6
 1, 13, 136, 13610, 1361015, 136101521, 13610152128, 1361015212836, 136101521283645, 13610152128364555, 1361015212836455566, 136101521283645556678, 13610152128364555667891, 13610152128364555667891105, 13610152128364555667891105120 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS There are only 2 primes i.e. 13 and 136101521 known in the sequence for first 1000 terms of the sequence. REFERENCES Shyam Sunder Gupta, Smarandache Sequence of Triangular Numbers, Smarandache Notions Journal, (to appear in Vol. 14, 2003). LINKS EXAMPLE a(3)=136 because 1, 3, 6 are first 3 triangular numbers. MAPLE a:= proc(n) a(n):= `if`(n=1, 1, parse(cat(a(n-1), n*(n+1)/2))) end: seq(a(n), n=1..20);  # Alois P. Heinz, Jan 13 2021 MATHEMATICA Table[FromDigits[Flatten[IntegerDigits[Table[n*(n+1)/2, {n, 1, m}]]]], {m, 1, 20}] CROSSREFS Cf. A000217. Sequence in context: A069511 A052262 A065550 * A123299 A142017 A157950 Adjacent sequences:  A078792 A078793 A078794 * A078796 A078797 A078798 KEYWORD base,easy,nonn AUTHOR Shyam Sunder Gupta, Jan 10 2003 STATUS approved

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Last modified January 26 18:20 EST 2022. Contains 350599 sequences. (Running on oeis4.)