A372292 Numbers that occur more than once in the odd bisection of A371094.

21, 117, 213, 309, 341, 405, 501, 597, 693, 789, 885, 981, 1077, 1173, 1269, 1365, 1461, 1557, 1653, 1749, 1845, 1877, 1941, 2037, 2133, 2229, 2325, 2421, 2517, 2613, 2709, 2805, 2901, 2997, 3093, 3189, 3285, 3381, 3413, 3477, 3573, 3669, 3765, 3861, 3957, 4053, 4149, 4245, 4341, 4437, 4533, 4629, 4725, 4821, 4917

Offset

1,1

Comments

Numbers that occur more than once in array A371100.

Links

Antti Karttunen, Table of n, a(n) for n = 1..15532

Example

21 is present because A371094(1) = A371094(3) = 21.
87381 is present because A371094(85) = A371094(213) = A371094(7281) = A371094(14563) = 87381.
185685 is present because A371094(469) = A371094(15473) = A371094(30947) = 185685.

Prog

(PARI)
A371094(n) = { my(m=1+3*n, e=valuation(m, 2)); ((m*(2^e)) + (((4^e)-1)/3)); };
isA372292(n) = if(!(n%2), 0, my(c=0); forstep(k=1, n, 2, if(A371094(k)==n, c++)); (c>1));
(PARI)
search_up_to = 1398101;
A371094(n) = { my(m=1+3*n, e=valuation(m, 2)); ((m*(2^e)) + (((4^e)-1)/3)); };
A372292list(up_to_n) = { my(v=vector((1+up_to_n)/2), x, lista=List([])); forstep(k=1, up_to_n, 2, x=A371094(k); if(x <= up_to_n, v[(x+1)/2]++)); for(i=1, (1+up_to_n)/2, if(v[i]>1, listput(lista, i+i-1))); Vec(lista); };
v372292 = A372292list(search_up_to);
A372292(n) = v372292[n];

Crossrefs

Setwise difference A372290 \ A372291.

Cf. A144864 (subsequence after its initial 1), A371094, A371100.

Sequence in context: A121628 A306532 A219154 * A054257 A341570 A297316

Adjacent sequences: A372289 A372290 A372291 * A372293 A372294 A372295

Keyword

nonn

Author

Antti Karttunen, Apr 26 2024

Status

approved