A078278
a(n) is the number from which if odd-positioned digits are deleted then one gets the concatenation of first n prime numbers, while if even-positioned digits are deleted then one gets reverse concatenation of first n prime numbers. Position of least significant digit is considered to be 1.
Original entry on oeis.org
22, 2332, 253352, 27355372, 213157751312, 2133517117151332, 21375173111117351372, 213951771113113117751392, 2233517911171133117117952332, 22395273111911371173119127352392
Offset: 1
a(4) = 27355372: deleting alternate digits starting from the LSD leaves 2357. Deleting the other ones leaves 7532.
More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 19 2003
A078279
a(n) is the number from which if odd-positioned digits are deleted then one gets the concatenation of first n composite numbers, while if even-positioned digits are deleted then one gets reverse concatenation of first n composite numbers. Position of least significant digit is considered to be 1.
Original entry on oeis.org
44, 4664, 486684, 49688694, 416089981604, 4162819019081624, 41648192110019281644, 416581941102112019481654, 4166819511041122114019581664, 41688196110511241142115019681684
Offset: 1
a(4) = 49688694: deleting alternate digits starting from the LSD leaves 4689. Deleting the other ones leaves 9864.
More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 19 2003
Original entry on oeis.org
2, 212, 22122, 2258577, 18913180982, 189219046321892, 1893099641364512802, 18935542777368728158257, 189400886865505550637253712, 1894918005023238233732500894622, 19367362777550568701870550728176482, 193719500503687550659615507369001321937, 1937649596364149143005250529144645910417392
Offset: 1
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a(n) = {my(c=vector(n), d=0, v=w=[4]); forcomposite(i=4, 4*n, c[d++]=i; if(d==n, break)); for(i=2, n, v=concat(v, d=digits(c[i])); w=concat(d, w)); fromdigits(vector(2*#v, i, if(i%2, v[1+i\2], w[i/2])))/22; } \\ Jinyuan Wang, May 17 2020
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