A078891 Concatenate first n triangular numbers in reverse order.

1, 31, 631, 10631, 1510631, 211510631, 28211510631, 3628211510631, 453628211510631, 55453628211510631, 6655453628211510631, 786655453628211510631, 91786655453628211510631, 10591786655453628211510631, 12010591786655453628211510631

Offset

1,2

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)=631 because 6,3,1 are first 3 triangular numbers in reverse order.

Maple

a:= proc(n) a(n):= `if`(n=1, 1, parse(cat(n*(n+1)/2, a(n-1)))) end:
seq(a(n), n=1..20);  # Alois P. Heinz, Jan 13 2021

Mathematica

Table[FromDigits[Flatten[IntegerDigits[Table[n*(n+1)/2, {n, m, 1, -1}]]]], {m, 1, 20}]

Crossrefs

Cf. A000217.

Sequence in context: A028013 A028073 A089758 * A078914 A068147 A025009

Adjacent sequences: A078888 A078889 A078890 * A078892 A078893 A078894

Keyword

base,easy,nonn,less

Author

Shyam Sunder Gupta, Jan 10 2003

Status

approved