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A225884 Triangular numbers whose binary and decimal reversals are also triangular numbers. 0
0, 1, 3, 6, 120, 153, 300 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

A subsequence of A061455.

a(8), if it exists, is > triangular(10^11) > 5*10^21. - Lars Blomberg, Jan 11 2016

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

BinaryReverse(120) = 15, DecimalReverse(120) = 21. Because 120, 15 and 21 are triangular numbers, 120 is in the sequence.

PROG

(C)

#include <stdio.h>

#include <stdlib.h>

#include <math.h>

int isTriangular(unsigned long long a) {

    unsigned long long sr = sqrt(a*2);

    return (sr*(sr+1) == a*2);

}

int main() {

  unsigned long long n, tn, t, r;

  for (n = tn = 0; tn < (1ULL<<63); tn += ++n) {

    for (r=0, t=tn; t; t>>=1)  r = r*2 + (t&1);

    if (isTriangular(r)==0) continue;

    for (r=0, t=tn; t; t/=10)  r = r*10 + (t%10);

    if (isTriangular(r)==0) continue;

    printf("%llu, ", tn);

  }

  return 0;

}

CROSSREFS

Cf. A000217, A061455.

Sequence in context: A157536 A046488 A074880 * A115647 A019437 A291982

Adjacent sequences:  A225881 A225882 A225883 * A225885 A225886 A225887

KEYWORD

nonn,base,more

AUTHOR

Alex Ratushnyak, May 24 2013

STATUS

approved

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Last modified December 16 19:11 EST 2018. Contains 318188 sequences. (Running on oeis4.)