A078795 Concatenate first n triangular numbers.

1, 13, 136, 13610, 1361015, 136101521, 13610152128, 1361015212836, 136101521283645, 13610152128364555, 1361015212836455566, 136101521283645556678, 13610152128364555667891, 13610152128364555667891105, 13610152128364555667891105120

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

Table of n, a(n) for n=1..15.

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