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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 EXAMPLE BinaryReverse(120) = 15, DecimalReverse(120) = 21. Because 120, 15 and 21 are triangular numbers, 120 is in the sequence. PROG (C) #include #include #include 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 October 14 01:36 EDT 2019. Contains 327994 sequences. (Running on oeis4.)