A078795 Concatenate first n triangular numbers.

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

Offset: 1

Author

Shyam Sunder Gupta, Jan 10 2003

Keywords

• base
• easy
• nonn

Comments

There are only 2 primes i.e. 13 and 136101521 known in the sequence for first 1000 terms of the sequence.

Examples

			a(3)=136 because 1, 3, 6 are first 3 triangular numbers.
		

References

• Shyam Sunder Gupta, Smarandache Sequence of Triangular Numbers, Smarandache Notions Journal, (to appear in Vol. 14, 2003).

Crossrefs

Cf. A000217.

Programs

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}]