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A080472 a(n) = smallest triangular number that is obtained by placing digits anywhere in n; a(n) = n if n is a triangular number. 1
1, 21, 3, 45, 15, 6, 78, 28, 91, 10, 171, 120, 136, 1431, 15, 136, 171, 1081, 190, 120, 21, 1225, 231, 2145, 253, 276, 276, 28, 2926, 300, 231, 325, 3003, 2346, 325, 36, 378, 378, 3916, 406, 741, 4278, 435, 4465, 45, 406, 4278, 1485, 496, 1540, 351, 528, 153, 1540 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Michael S. Branicky, Table of n, a(n) for n = 1..10000

PROG

(Python)

from math import isqrt

from itertools import count

def dmo(n, t):

if t < n: return False

while n and t:

if n%10 == t%10:

n //= 10

t //= 10

return n == 0

def a(n):

return next(t for t in (i*(i+1)//2 for i in count(isqrt(2*n))) if dmo(n, t))

print([a(n) for n in range(1, 77)]) # Michael S. Branicky, Jan 21 2023

CROSSREFS

Cf. A068164, A068165, A080470, A080471.

Sequence in context: A218249 A040433 A317321 * A118389 A077690 A018855

Adjacent sequences: A080469 A080470 A080471 * A080473 A080474 A080475

KEYWORD

base,nonn,changed

AUTHOR

Amarnath Murthy, Mar 07 2003

EXTENSIONS

More terms from Ray Chandler, Oct 11 2003

STATUS

approved

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Last modified February 3 12:24 EST 2023. Contains 360035 sequences. (Running on oeis4.)